I've seen these before, but an archive search reveals that it hasn't been on PackyHumor yet. Thanks to Kat Costello for sending this one along...

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 gone out.
4. - If your children speak to you in Latin or any other language which they should not know, shoot them immediately. It will save you a lot of grief in the long run. However, it will probably take several rounds to kill them,so be prepared. This also applies to kids who speak with somebody else's voice.
5. - When you have the benefit of numbers, NEVER pair off or go alone.
6. - As a general rule, don't solve puzzles that open portals to Hell.
7. - Never stand in, on, or above a grave, tomb, or crypt. This would apply to any other house of the dead as well.
8. - If you're searching for something which caused a loud noise and find out that it's just the cat, GET THE HELL OUT!
9. - If appliances start operating by themselves, do not check for short circuits; just get out.
10. - Do not take ANYTHING from the dead.
11. - If you find a town which looks deserted, there's probably a good reason for it. Don't stop and look around.
12. - Don't fool with recombinant DNA technology unless you're sure you know what you're doing.
13. - If you're running from the monster, expect to trip or fall down at least twice, more if you are female. Also note that, despite the fact that you are running and the monster is merely shambling along, it's still moving fast enough to catch up with you.
14. - If your companions suddenly begin to exhibit uncharacteristic behavior such as hissing, fascination for blood, glowing eyes, increasing hairiness, and so on, kill them immediately.
15. - Stay away from certain geographical locations, some of which are listed here: Amityville, Elm Street, Transylvania, Nilbog (you're in trouble if you recognize this one), anywhere in Texas where chain saws are sold, the Bermuda Triangle, or any small town in Maine.
16. - If your car runs out of gas at night on a lonely road, do not go to the nearby deserted-looking house to phone for help. If you think that it is strange you ran out of gas because you thought you had most of a tank, shoot yourself instead. You are going to die anyway, and most likely be eaten.
17. - Beware of strangers bearing tools. For example: chain saws, staple guns, hedge trimmers, electric carving knives, combines, lawn mowers, butane torches, soldering irons, band saws, or any devices made from deceased companions.
18. - If you find that your house is built upon a cemetery, now is the time to move in with the in-laws. This also applies to houses that had previous inhabitants who went mad or committed suicide or died in some horrible fashion, or had inhabitants who performed satanic practices.
19. - Dress appropriately. When investigating a noise downstairs in an old house, women should not wear a flimsy negligee. And carry a flashlight, not a candle.
20. - Do not mention the names of demons around open flames, as these can flare suddenly. Be especially careful of fireplaces in this regard.
21. - Do not go looking for witches in the Maryland countryside.