I think it's pretty safe to say that Ridley Scott's Alien belongs on just about everyone's top ten list of horror films. The 'haunted house in space' story of a rag-tag group of blue collar space truckers who unknowingly bring aboard a hostile organism has been imitated countless times since its release date in 1979. I actually prefer James Cameron's space-action sequel, but there's no denying the power and authenticity the original had to scare the crap out of you.
It also had some very effective marketing in the form of one of the greatest movie trailers of all time. I remembered it was pretty good, but finding it again on YouTube allowed me to study it, and realize that it has become what all action/horror trailers follow today. Even on our smaller level, crafting a great trailer can be the viral push you need to attract a lot of attention, and the Alien trailer is a good template. For example:
The Use of Elements Not in the Film
One thing that everyone seems to remember is the cracking egg. While there were alien eggs in the film, they looked nothing like the chicken egg featured in the trailer. Oddly textured and sitting on a strange landscape, this was a bizarre image (also featured on the movie poster) that seemed to contain something terrible waiting to emerge. The light coming out of the inevitable crack helped cement this notion. We also get music that is creepy and haunting, again something found nowhere in the actual film.
Build Up to an Explosion
When the egg cracks, the imagery changes (notice the visual link between the lights) and we get that distress signal wail sound that immediately gets under your skin. Random shots from the movie are flung at us, which don't really tell us anything, but do convey a lot of dread. We see closeups of faces, space explorers searching a foreign environment, and Sigourney Weaver running for her life. Just when things build to a head, all hell breaks loose and we get faster cutting, apparent violence, and alarming screeches of what we assume is the terrible Alien of the title. It's incredibly effective.
Silence and a Great Tagline
Then all goes quiet and we get a extreme wide shot of space centered on a tiny ship with the unforgettable line "In space no one can hear you scream." Wow.
And there you have it, the perfect recipe for the horror-thriller trailer. Remember to pick the most visual elements of your movie, create some new ones, slap them all together with an overpowering score and nail the coffin shut with some great writing. And don't go over two minutes. You don't need to.