Thanks for the link. However, I find it pretty hard to make a trailer for a 15 min. short, without giving too much away. Thinking about it, I actually don't care much for trailers when they are too "selling" and almost follows a predetermined pattern. And, of course you are right in that it should sell. I just have a hard time thinking of how to make my short be like that. Perhaps I'll give it a try.
Go watch the trailer for The Conjuring... then go watch the Conjuring... every single scare in the movie is included in the trailer.
If you don't actually care about trailers "selling" and "following a predetermined pattern" then you should consider just making art films.
That's not to be harsh... that's the reality of show BUSINESS.
For a short, you don't need a 2 minute trailer. Try cutting a nice quick 30 second commercial and if you haven't yet (and you really really should before you write your script), get to know your target market.
Look at House at the End of the Street... sold as horror in the trailer but nothing more than a thriller in reality.