A recent issue of the New Yorker has a great article giving insight into how Hollywood markets the indie films we all hear about. This is not DIY-level grassroots marketing, this is big money Indiewood bru-ha-ha.
But there's a lot we can learn from them, including the focused strategic thinking on the poster and the trailer, which are key for us as well.
Definitely worth a read: The Cobra: Inside a movie marketer's playbook.