One of the most important things to consider when creating a character or preparing to write one in a story is his or her (or its!) desires. Everyone wants something, and if your characters don't want something, their story is likely to be fairly boring. Desire creates conflict, as Character A thwarts, deliberately or accidentally, Character B's wants. Conflict makes stories. Well, interesting stories. You could write about how Character B sat around in his underwear all day and ate Cheese Doodles, or how she decided to stay home and paint her nails instead of going after the bad guy. But that's not going to be something your readers want to read for very long.
I'm working on a post or two about the work of some of my favourite addictive authors, like Jim Butcher and Janet Evanovich. Authors who write stories I just can't put down, those books that keep me up until 2 in the morning because I just have to know what happens next! What is it about your favourite stories that compels you to keep turning pages? It's a personal experience, and it varies by reader, but there are common elements to a story that won't be set aside. I'll be looking at those from my own point of view later on.
I also want to get into talking about editing and revising in-depth. I have a bunch of stories on my hard drive that have been written over the last fifteen years. I have no plans to do anything with them, but they might make good examples. Just in looking them over while writing this, I've seen bits that make me cringe and bits that remind me very much of stuff I'm writing these days. So look for that.