1. Brush up on your serial killers. Many writers base their novels on real-life events, and find this subject fascinating. I found myself on the first day sitting next to Dallas Mayr (Jack Ketchum) and was able to successfully entertain him with tales of a serial cannibal I once knew. These kinds of sure-fire conversation starters are key to any horror convention.
2. Pick a side: Lovecraft or Poe? You just can't be ambivalent about this topic. If you're going to go to a convention of writers, you'd better love one and hate the other, and be able to defend your side vehemently. Otherwise, Darryl Schweitzer will peg you as an imposter faster than you can say "Cthulhu."
3. Watch as many obscure scary movies as possible before attending. The only thing horror writers like more than a creepy story is a scary movie. There also seems to be a tendency among this group to find the most ambiguous film ever made and make you feel like a giant lump of stupid if you haven't seen it. Heard today over lunch: "You haven't seen 'When Hell Comes to Frog Town'? It's only Rowdy Roddy Piper's best cinematic performance of his career. I'm sorry, I can no longer continue speaking to you, you giant lump of stupid."
4. Be prepared to have your favorite Stephen King novel completely skewered. Another popular activity for horror writers: espousing on why Stephen King is a hack. You thought The Stand was fabulous? Blind meadow voles could sniff out a better novel. Did you find Bag of Bones entertaining? You are an incompetent boor who should be eaten alive by blind meadow voles. Why on earth would you be so foolish to think that the most popular author on the planet could actually write a good story? (I suspect this is such a favorite activity among horror writers because they might be a tad jealous. However, this has not prevented me from trashing Under the Dome in select circles.)
There you have it: a primer on blending in among horror's literary elite. I would write some more tips, but I am currently being dragged outside and tied to a stake so that I can be eaten alive by blind meadow voles.