In relation to my last post, Tess Gerritsen has a wonderful blog on how to write second drafts. You can find it at Tess Gerritsen's Blog. She makes six main points on "how to" and it's well worth a read.
Are you a "pantser" or a "plotter"? Right now, I think I'm relying on my plotting sketch to stick in another sub-plot, plus pump up my villainess. In the past, I've just sat down and let it fly. I think either way is good, depending on your WIP and what stage you're at in it.