(I don't have any idea where this came from, but I received it on a print-off and liked it enough to type it up again. I've edited it a bit as well. Some good advice for life—particularly continuation of said phenomenon.)
When it appears that you have actually killed the monster, never stop to check if it's really dead. If you have the ammunition, keep pumping bullets into it. Remain at a safe distance.
If you find out that your house is built on or near a cemetery, was once a church used for black masses, had previous inhabitants who went mad or committed suicide or died in some horrific fashion or who practised necrophilia or performed satanic rituals; move away immediately.
Never read aloud a book of demon summoning, even as a joke.
Do not search the basement; especially if the power has just gone off.
If your children speak to you in Latin or any other language which they should not know, or if they speak to you in a voice which is not their own or sounds long-dead, shoot them immediately. It will save a lot of grief in the long run. Be prepared to use several rounds.
When you have the benefit of numbers, don't split up to search.
As a general rule, don't solve puzzles which open portals to Hell.
Never stand in, on, above, beside or anywhere near a grave, tomb, crypt, mausoleum, or other house of the dead. Do not take anything from corpses you find.
If you're searching for whatever made the strange noise and discover that it's just the cat, it probably isn't.
If you find a town which looks deserted, it's probably for a reason. Take the hint: Stay away.
Don't fool with recombinant DNA technology unless you know what you're doing.
If you're running away from a walking corpse, expect to fall down or trip at least twice, more if you're of the female persuasion. Also note that, despite the fact that you are running and the monster is merely shambling along, it's still moving rapidly enough to catch up with you.
If your companions begin to exhibit uncharacteristic behaviour all of a sudden, such as hissing, fascination for blood or pain, glowing eyes, increased hairiness and so forth, get away from them as fast as possible.
Stay away from certain geographical locations, some of which are: Amityville, Elm Street, Transylvania, Nilbog (God help you if you recognise this one), the Bermuda Triangle, or any small town in Maine.
When your car runs out of gas at night in a strange neighbourhood, do not go to the nearby deserted-looking house to phone for help.
Beware of strangers bearing tools such as chainsaws, staple guns, hedge trimmers, electric carving knives, lawnmowers, butane torches, soldering irons, butchers appareil, or any device made from recently-deceased companions.
Listen closely to the soundtrack; and pay close attention to the audience, since they are usually far more intelligent than you could ever hope to be.