If you had to give one piece of advice that is pretty much universally applicable, what would it be?
I wouldn't dare defile Douglas Adam's memory by not mentioning that you should keep a towel with you at all times, but my second contender is a surprisingly short three-parter:
yeah that doesn't work unless you don't have bosses or multiple levels of bosses who only care about making Numbers on their already sheet look like what they want them to look like