Make it a point to subtly acknowledge the genre's history and biggest cliches.
Lesson learned from: Scream (1996), The Cabin in the Woods (2012), You're Next (2013)
Horror fans appreciate it when filmmakers share their enthusiasm for the genre and their knowledge of its past. Moreover, they'll salute the hell out of someone's horror-comedy if it's loaded with intelligently executed and well-placed subversions and/or riffs on of the genre's most overused tropes. It shows that the screenwriter and director aren't just some paycheck-cashing hacks who want to exploit the horror community's viewing interests. It implies, "Hey, these filmmakers really know their shit," and it's rather comforting.
A prime example of this is last year's The Cabin in the Woods, an aggressively meta horror-comedy that hinges on the audience's understanding of the genre's history and its myriad monsters, ghoulies, and creepers.
Without giving anything away here to those who've yet to experience co-makers Joss Whedon and Drew Goddard's brilliant film firsthand, let's just say that The Cabin in the Woods expects you to know about Asian horror cinema and comprehend the fact that Hollywood has rebooted all of the classic Universal Monster movies except The Creature from the Black Lagoon. Otherwise, some of the film's smartest bits won't connect.