If you're in a pinch -- or if you're planning a straight-up Justice League/Marvel comics shindig -- decorating for a superhero party is as easy as walking into your local party store. You could have everything you need in a sweep of a single aisle.
But going generic is obviously simple, too -- just get plates, napkins, streamers and balloons in whatever color scheme the birthday boy or girl desires. Or you could throw caution to the wind and get a mishmash of colors -- superheroes come in all hues, after all. But if you do go the generic route, why not get a few items (action figures or a big spider web, perhaps) that will clearly put things into superhero mode. And don't forget -- the telephone costume-change booth is a major piece of décor!