How do you explore a new city as a tourist?

I just walk and see what I find. I like walking so that’s a plus.
As the others have said, anything you Google is going to be too popular. Just wander and wonder.
- Tbh now that i think about it, wouldn't a hoverboard be the perfect mode of transport for exploring cities? It's faster than walking but still slow enough that you can take things in and stop easily, saves you from getting an extremely chiseled ass from all the walking, and you can easily just tuck it under an arm when needed.

Unrelated to your question, but you seem to have ticked the option in your settings that indicate that you are a bot, so anyone with a blanket ban on bots won't see anything you write.
- I know, I don't know how to change that... It was a mistake :(
  
  log into lemmy.world, ideally from a browser, not an app or a frontend, click your account in the top-right and choose settings. Then it's this one:

I (almost) never make any plans. I travel to the city, and then I decide what to do on the spot. Whatever I happen to be in the mood for. Most places I visit have something I want to see already and I don't have to plan for it. And if there are night life activities, I'm checking them out. No rules. No itinerary. Just spontaneous adventure.

I personally make sure I stay in a good neighborhood and check Wikivoyage for details like transportation and safety, but that's pretty much it. If I land in a good neighborhood (not touristy, lots of amenities and restaurants around, easy connection on foot or by public transport to the major areas), then I'm pretty much golden.
It's a bit counter-intuitive, but I think not enough research is much better than too much. Any tourist information will draw you to overpriced and/or overhyped places. The desire, say, to "eat the best X" or "visit the most famous Y" is making your travels crappier.
Instead, I recommend cultivating normalcy. Visit your neighborhood by foot, and take chances on unknown places. You can check Google Maps to get the sense of a place, but if the reviews are good and they're mostly local reviewers, and the place is crowded, you're in good hands. Check out what other people are eating and order that. (Just point if needed.)
My partner and I have what we call our "grounding ritual." We set out by foot in our neighborhood and spot what we'll need: a convenience store for late-night snack runs, a supermarket or fresh market for food, etc. We check out public transportation options nearby. Then we find a nice, no-frills local restaurant and have a meal there. If the place is good, we make a point of returning there over the next few days. Doesn't matter if we're there for a weekend.
We just returned from a few days in Warsaw, a city I had never been before. Besides the Old Town, none of the places we visited were stuff I had read about online. We just let our feet, eyes, and noses lead us to interesting places.
- This is AWESOME advice. I have no problem hitting up tourist spots but they can be a bit much (and sometimes hugely overrated). I try to balance those out with just living in the city eating and drinking away from all the popular spots too.
  If the place you're visiting has good public transit, I've also found that I strangely enjoy riding trains and buses to random places. It's a good way to immerse yourself and get off the beaten path.

Last time I was on vacation alone I googled the few things I knew I wanted to see/do, and the rest of the time I just went out and see where I end up. Looking where locals go and do that is also a great trick.
My experience is that most easily online findable things are very tourist-y. I preffer to see more of the non-tourist stuff. Knowing a local is then the best, but by lack there off, just go with the flow.

I like to aimlessly walk around and see where I land.

Check the neighborhood maps on nomadlist. Check out where there are supposed to be cool stuff/people. Usually I just search Google maps for things/streets in those neighborhoods for things that might be interesting.. Cafés, restaurants, bars, shops, etc..
You MUST get used to meeting locals when you're traveling a lot. Meetup.com, couchsurfing, internations, dating apps, or even the hostel where you are staying.
For context, I traveled full time, nonstop for 4ish years before covid. This is how I did the majority of my travel. Things like attractions or museums or historical places get really old really fast. If I never set foot in an art museum for the rest of my life, I will not be upset in the slightest. People, food, shopping, culture.. This is the only thing I feel is worth seeing anymore.

I've traveled to many corners of the planet and have a different take than most. Many people try to min/max their trip, filling up every minute of every day which doesn't appeal to me at all. I prefer a laid back, impromptu schedule to give myself time to see and do stuff I didn't plan and time to breathe and enjoy being in a new place. To me, the worst thing you can do is overplan and overschedule so you're stressed out if something happens to screw up your tight schedule.
As for selecting what to do, I usually do tons of internet and book research finding things that sound interesting. I add everything to a list and to Google Maps as saved points and then try to cluster them into days, making sure I'm not packing in too much as noted above. I'm not especially concerned if I don't get to everything--if I really enjoyed a place, odds are I'll return and put focus on different experiences.
- This is approximately what I do as well, and would highly recommend. The one caveat I would add is while you are researching things you might want to do, take note of the subset of things you most want to do, and make sure you know what days/times they are open, if you need to book in advance, etc. I am very against having a hard schedule, but I also don't want to travel somewhere only to miss the one thing I was really looking forward to because I decided "I'll do that tomorrow," only to find out it was closed the next day.
  An additional pro-tip: Make your first list of things you might want to do ahead of time, and name it after the place you are going, e.g. "New York." Then while you're traveling, make a second list of "favorites", e.g. "New York Favorites." Keep track of all the restaurants, activities, view points, etc that you enjoyed using that second list. Then whenever someone asks for recommendations for a particular location, you can just send them your favorites list.
  
  Great point about making sure places are actually open when you want to go. I think I've taken it for granted that a large majority of the places and things I typically want to see have regular-ish business hours or are open 24/7 (e.g., something in a park or other public space).

Urban hiking. Plan a few stops at big tourist attractions and then walk between them, stoping for drinks and food as desired. Easily the best way to actually explore different neighborhoods.
- Definitely walking walking walking. Can be hard depending on the city, but even if you transit between neighbourhoods and spend time walking around then individually, it's a great way to feel a city.

I find the best way is to establish where the main thoroughfare is, and also the old part of town. That's usually where there's shops and nice places to wander about window shopping and looking for food options. Bigger cities often have multiple versions of these things so you might need to walk around a few to get a sense of which ones are touristy and which ones are something else.
Once you sort of have your bearings, think about what this place is famous for in the sense of "when have you heard about this place in an everyday context?". Was there a famous guy who did stuff here? Did something big happen during the industrial revolution? What was the war situation like? If there's any big notable things that spring to mind, chances are there's a museum or monument or thing about it. And obviously what springs to mind is going to be different for different people. You might instantly go to some botanist who worked for the national gardens while I might think of some architect who designed a bunch of metro stations, while someone else thinks of that really well preserved tank they have. Don't go "I have to go to these places because they're famous", go "oh that's where that I thing I know is!"
Alternatively, super niche but if you still use Pokemon go/Ingress, open it up and see where portals are scattered. Generally speaking if there's a lot of portals in one area, there's something interesting there. Also idk about Pokemon go but ingress has a 'missions' mode where people make little pseudo-orientering maps where you have to run about looking for a specific location, and they're often themed.

Get to know a taxi driver. Ask locals where to go and what to see. Stop by a visitors bureau or welcome center. Hit up a local colleges student center.
When I traveled a lot, I used to start with the local phone book. Not only did it have business information, but government info, and a section devoted to local arts and museums. These days I (gasp) talk to people at pubs or bars or coffee shops. Obviously, if they are annoyed, I let them be, but you'd be surprised how many people are happy to brag about their community.
- That advice wouldn't fly in my neck of woods, as no local would even think of using a taxi, unless they have exhausted any other option. Sorry, the driver is too busy scamming tourists, right now.

It depends on a lot of things. Which part of the world? In Europe big cities all have the tourist part and the "old town" part. If you are there sightseeing just get a tourist map and start exploring.
You can usually get an equivalent of a tourist day tickets, which will give you unlimited access to public transport, sightseeing buses and some attractions/museums. Just pick up the one which tickles your fancy and usually you can get it from any airport, big train/bus station when you arrive.
If you are there to party and check out the night life I would strictly stick to popular spots.
For any other interests (hiking, historical spots, etc) you can find a city specific list of recommendations online.
Also it usually helps to google which tourist scams are popular in the region to avoid them.
- In Europe big cities all have the tourist part and the "old town" part.
  To add on to this. Quite often there is a neighborhood that is a bit away from the touristic center, a bit more shabby, used to be 'bad' part of town. Often those are more vibrant with less tourist traps and fun bars and restaurants that are visited by the locals.
  I tend to look out for that kind of neighborhood.
- The one tourist and one old town part isn't true for Berlin though. As it used to be multiple towns fused together over time, there are multiple old towns (as long as they aren't destroyed from the war), and quite a few touristic areas scattered all over the city.
  
  Fair enough. I should add my comment is not universally true for all European cities but to be fair we still don't know where OP is planning to go.

In each city I visit, I always try to do a bike tour. You can see a lot in a 2-3 hours and the tour guides are usually very knowledgeable.

I use a lot of Google Maps to tag things I want to see. From that, you'll usually get a cluster of things in an area that you want to see.
I also don't really care about what the articles say more than just getting a basic list of ideas and then looking it up on Google Maps to see what people really think of it.

I like to just to Geocaching. There are often a lot of caches in the cities, and a lot of then often have really niche information on I teresting topics. Plus when doing earth or virtual caches, you often need to explore quite a bit.

My wife and I have traveled all over Europe the past 10 years. For every area we go to, we pick up a Rick Steves travel book and it has been amazingly helpful. The beginning of each book gives a few recommended timelines of how long to spend in each city/area. For each city it does a great job sorting through the bullshit tourist traps. The recommendations are tiered (must see, see if you have time, see if the attraction might be specifically interesting to you). This really helps with prioritizing and helps you figure out how much time to spend in an area. There are also great recommendations for restaurants and lodging which is especially helpful since TripAdvisor isn't what it once was. Well worth the $20 for a book, can't recommend it enough.
I also agree with what others said. Find a pub and chat with the locals. Happy travels!

I love to get lost and explore on my own. Sometimes I look up some interesting places to visit, museums, pubs and stuff. It is better to do this on your own or with small group (max 4 people). If you want some tips for Czech Republic you can ask me :-)
- I do this too when solo travelling. Gives you a good feel for the city I think.

My wife and I love to visit new places. We will generally prepare by asking friends who have visited what they liked and disliked, I would check the areas affiliated subreddit to get guidance from the locals, and do a little online searching to get a general feel for the city.
Once there don't be afraid to talk to people. Talk to a can driver, spark up a conversation at a cafe. Locals are almost always willing to share their favorite places with you since you're a visitor to their city and they want to shed it in the best light.

I love to go on free walking tours if they're available. Other than that there is a view of most popular attractions on Google travel which you can filter by most popular for tourists or locals.

Reading comments here to find a better way, but we just walk or take a train or subway and get off and walk and see what we find. Talking to locals helps too, as they will tell us about places they are proud of and think we should see. We have stumbled on really cool places most tourist do not find or ended up riding paddle boats in a park. We do research ahead of time and have a list of places we do not want to miss.
This does not always work. Some places are too big and lack public transportation. We have had to return to a train station a get a cab to a local attraction (Dover, UK).

I just go for a run! Usually early in the morning Strava usually has some routes for most of the places I go and It’s a great way of seeing some of the sights! I’ve found some great bars and places to visit later on with my wife when on holidays this way.

I need to eat.

Go on a paid pub/bar crawl. They’re super cheap and you’ll meet other travellers/locals

How are you choosing your destinations in the first place? There just be a reason you're traveling to these places, especially as you state it's specifically for tourism. Wouldn't it make sense to do/see the things that attracted you there in the first place?

I usually read a lot about the city in advance and make a list of sights I want to see. And most time I use to stay at least one night. So I arrive the first day and use to walk around the city. In most of the cities (except Berlin) most of the sights are near to the city centre. So most parts of my list are done without any planning. For the next day I only have few sights left. Mostly things apart the centre or indoor activities like museums.

I search for the types of things I like specifically instead of the things that are thought to have wide appeal. Wherever I go I look for: vegan food, extreme metal concerts, goth clubs, swinger clubs, anime/gaming stores, and the occasional park with a nice lake or river. Do the same but with your interests! All cities are mostly similar to each other in a lot of ways. Also, you can spice it up by trying to do one or two things that are unique to that city's culture without being tourist traps, such as a local food item or a particularly good museum or coffee shop.

Go to local antique shops/flea markets. Cool people and cool old shit

Im a bit of a film nut, so I search for "Films shot in place" and see if theres anything that jumps out at me. When I was in Paris/Europe I went to a bunch of Filming locations from Ronin.