- What is the main character's goal for this particular scene?
- What is the conflict (i.e., what stands in his/her way, and where is the tension/suspense, even if it's minor/internal)?
- What does the reader learn from this scene? Not what sort of moral lesson, just what new, useful information does this scene impart?
- Does this scene really need to be here? Could I take it out without having much impact on the overall book? This is a tough one because sometimes the answer is yes and then I have to decide whether to add to the scene or just cut it.
- What emotion/mood am I trying to evoke with this scene? How do I want readers to feel (with the understanding that I can't control their actual reaction)?
- Why will readers care about this scene and the characters in it?
- Where is the theme?
Finding Theme in Your Book: An Exercise in Searching for Repeating Patterns
25 Things Writers Should Know About Theme
Once I finish answering all these questions I usually have several more (really good) ideas for improving the chapter. It forces me to think about the chapter as a cohesive whole, rather than nitpicking the words to death (which is also important, but less so in second-draft stage).
So there's my process. Hope it's somewhat helpful. It's also an evolving list, so any suggestions for things to add are welcome!