Step 1: Come up with an angle from which to promote the film and ensure that said angle features prominently in all pre-release promotional materials including fan-oriented press releases and interviews with talent.
For example, suggest that Guardians of the Galaxy is very similar to the original Star Wars as a way to (i) cross-promote two franchises that are owned by the same multinational corporation, (ii) get-over any (Green Lantern-inspired) resistance the target audience might have to a space-based action movie by comparing Guardians of the Galaxy to a film they already know, and (iii) give the adult audience an excuse to infantilise themselves and set aside their cynicism by inviting them to approach Guardians of the Galaxy in the same way as they approached Star Wars as children.