The current issue of Rue Morgue Magazine, the issue with the Grindhouse cover, has a wonderful article by Hershell Gordon Lewis entitled "How to make an exploitation film" that should be required reading for anyone making and/or distributing an independent movie of any kind.
He never says it directly, but the article is about taking your independent movie and marketing it in a way that shows what it does that mainstream movies can't or won't do. This is one of the reasons that the '70s and '80s did so much damage to the independent genre movie; the big guys started making their own exploitation movies.
Looking at most trailers for independent movies, especially genre material but certainly not limited to it, they do nothing to separate themselves. They look like cheap versions of a Hollywood movie... and depressingly often, they are. It may be more of a challenge, perhaps, nowadays to make a movie that's appealing to a significant audience and also looks like something that Hollywood isn't already doing with better (or, in many cases, "better") production values and more familiar actors.
Our job, as I see it, is to find the marketable things that Hollywood isn't giving people and not only find ways to get them into our movies, but let people know we did. That's the legacy of those old Grindhouse (and pre-Grindhouse) guys and right now we're largely ignoring that (rather obvious) wisdom.