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:
- never lie.
- never tell the whole truth.
- never pass up a chance to use a real bathroom.
Excellent, I’m going to add to this, even if the the answer justifies/requires an explanation put the answer first ie “Yes, long explanation” is vastly superior to “Long explanation, so yes”