1. When it appears that you have killed the monster, never check to see if it's really dead.
2. Never read a book of demon summoning aloud, even as a joke.
3. Do not search the basement, especially if the power has just gone out.
4. Never accept invitations from strangers, especially individuals who inexplicably live in isolated areas and have no contact with society.
5. As a general rule, don't solve puzzles that open portals to Hell.
6. If you're searching for the cause of a noise and find out that it's not just the cat, leave the room immediately if you value your life.
7. If appliances start operating by themselves, move out.
8. No sex, beer or partying! Any of these activities will surely seal your fate.
9. If you find a town that is deserted, it's probably for a reason. Take the hint and stay away.
10. Don't fool with recombinant DNA technology unless you're sure you know what you're doing.
11. Stay away from certain geographical locations, some of which are listed here: Amityville, Elm Street, Transylvania, Nilbog, the Bermuda Triangle, or any small town in Maine.
12. If your car runs out of gas at night, do not go to the nearby deserted-looking house to phone for help.
13. Beware of strangers bearing tools such as chain saws, staple guns, hedge trimmers, electric carving knives, combines, lawnmowers, butane torches, soldering irons, band saws, or any device made from deceased companions.
I wish I could take credit for writing these...