DON'T WORK WITH PEOPLE YOU HAVE A BAD FEELING ABOUT: I can not stress how dogmatically this should be adhered to enough.
Maybe it's the optimist in me, but I would change this to be "Work with people you have a good feeling about." Though, the underlying difference is that the original phrase implies that everyone is fine to work with until you've eliminated them, whereas I'm saying that I assume no one is good enough until I've cleared them.
Many a startup has been killed by this sort of up-with-people go-getter, who, with a (usually dumb) smile undermines this useful advice:
"Don’t deceive yourself about whether or not your users actually love your product."
"Ignore what the press says about you, especially if it’s complimentary."
IT'S NOT ABOUT NEGATIVITY OR POSITIVITY; IT'S A MATTER OF ACCURATE ASSESSMENT.