I typically start with a character with whom I would like to spend a great deal of time. He or she can be complicated and flawed, but must posses something interesting. Problem was, all my MC ladies were in a huge catfight for my brainspace. The aging ex-Playboy bunny knocked the over-stressed ad exec and the rest of them on their asses for a while, but now she's taken a back seat. Maybe she'll have her day, but for now she's filed under "Brainstorming.doc."
My agent gave me some sage advice, and with her help, I think I've picked a winner. The plot's pretty much down, so now for my favorite part--fleshing the MC out. Love this. It's like getting to know a cool new roommate, but you have a say in who she is and won't get stuck with a clunker. I'm fanatical about getting to know my characters before I write anything. She has her own dossier and I'm forming her style. After she simmers for a few more days, I'll get going. Can't wait.
How do you get started on something new?