My 2 cents.

Use only promotional shots from the film, but not of anything that doesn't appear in this edit. For example, don't use a still where Spock wears the yellow uniform because he doesn't in the film.

Don't use screen caps. Why bother if it can be seen within the film?

Present a different photo for each facet. Don't repeat any of the cover stills if, lets say, you're making an insert.

Don't use any solo stills of any crew member unless it's either all of them or they are pictured w/ either kirk or Spock.

Don't use any still on the spine. Keep it the title and studio logo.

Here's what I would suggest for the back cover photos

here you have one of Kirk and Spock but different enough (since Spock is not looking like his usual Starfleet self) to suggest seperate circumstances.

An action scene to suggest there actually is some in this movie.

And, of course, the star of the film, the Enterprise in a not so typical space shot. Also since this is a sci-fi film it gives you an fx scene.