My character in Sagiro's game has a whole collection of these, one or two of which KidCthulhu quoted. I'll edit the list to take out the obscure and campaign-specific ones:
1. Don’t tell the guard you’re going to go with him.
2. Avoid stealing stupid things.
3. Avoid the evil baker.
4. Don’t hit the monster with a bush.
5. A frontal assault is the fastest way to die.
6. Always club the mage first. <Note: party members wish the word “evil” inserted here.>
7. Heal first, chase and fight second.
8. Look at the ceiling. Yes, now!
9. Sigils are icky. Don’t read them.
10. Bad things come in big boxes.
11. Tie down the rope before jumping ship.
12. Look under the altar, or under whatever is heaviest.
13. Don’t try to leap over the monster. Yes, even this time.
14. When given freedom, take it.
15. If you seal a room shut, search it first.
16. Don’t sass the archmage or the assassin.
17. Look both ways before crossing the carriage-way.
18. Everything is funnier with a monkey.
19. Everything is our fault.
20. Ask for stuff. You never know.
21. Keep track of your adventuring buddy.
22. Low expectations make for a happy half-orc.
23. Don’t kill your best friends by mistake.
24. Please refraining from taunting the dire bear.
25. The PC with no diplomacy skill shouldn't offer condolences to the newly bereaved.