Okay, for those who have NOT seen the movie, including me, watch the trailers and teasers - you'll get a sense of what's going on. Also watch Batman Begins - it will help, though I don't think it is as gritty as the new movie.
Put simply, try to get a more of a "real world" glass and steel look and feel to your characters - not so much camp and wild costumes as have been seen in the earlier Batman movies or series.
Oddly, another movie I'd suggest watching would be Blade Runner for the same ambiance.
Hope that helps.
[EDIT] Updated the brief some - it can be one, two or three characters - however many you feel you can do!