The best thing to do is to have a trailer that doesn't show much at all but isn't misleading about what it is.
Prometheus's trailer sold tickets, that's for sure, but it also mislead people into thinking it was a deep and riveting sci-fi movie akin to 2001: A Space Odyssey, when it was basically just an above average 2 hour thriller with various themes shoe-horned in by Lindelof. :p