When I get seriously into revising something, I dig out the highlighters to help me find the dead spots, the ones that put the reader to sleep. I work on a chapter at a time and read, looking for a specific element in the story. Backstory is usually my first element. I highlight everything that's backstory in that chapter with a yellow marker.
Then I look for description and mark it in pink. Green is for exposition (explaining something to the reader), another good one to check for.
The object is to see at a glance what you've got. Does it stop the action or slow the story? It may depend on the kind of story you're telling, but I'm aiming for a fairly fast pace, especially in the opening scene. If I see much yellow or pink, indicating backstory and description, I know I have work to do.
Green is another flag—am I teaching the reader how to fly a helicopter or entertaining him? How much does she really want to know? The temptation to share all that valuable research you've done can be irresistible, but be strong. Resist.
All these elements slow the story, so they're included on a need-to-know basis. Does the reader need to know this to understand or follow the story? How does it apply to this scene or this action sequence? Is the information shown in small, bite-sized bits or is it a big chunk all at once? Is it broken up with action? These are things to think about.
What do you look for? Which elements put you to sleep? And how do you locate or mark those slow spots?