I work on six pitches and send them off to a publishing house to be considered. While waiting for them to get back to me on those pitches, I start working on four other books. One that was very nearly done and ready to be sent off to my agent. One that was part way through the first rough draft, and two more that are coming up the pipeline for when I finished the one almost ready to be sent off to my agent.
A couple months later, the publisher gets back to me and wants proposals for two of the pitches I sent them. Lots of work quickly follows as I put aside the other stories I'm working on and start writing the two proposals. (About 50 pages long each. 100 pages total.) A couple of months later, proposals are done and sent off and I go back and finish the manuscript that was close and send it off. I start working on the other three stories again. Months later, the publisher gets back to me and is especially interested in one of the proposals. They love it. A back and forth begins as they ask me if I'd be willing to make changes. I agree. Book is under consideration for another month or so and then out of the blue they decide they don't want it after all. Much weeping and wailing follows, before I pick myself up and march off to work once more.
Back to the drawing board for me. My agent and I regroup and decide that since there was so much interest in the two stories I wrote proposals for, I should switch over and finish writing the full manuscripts for both of those before returning to the other three stories. I start from scratch once again and begin writing two new stories from the start, with an occasional return to the other stories when I need variety. In the mean time, I work on four NEW pitches for some story ideas that have been percolating in the back of my mind for a while. My agent sends off the new summaries to a publisher and . . . on it goes.
Currently, I have two completed manuscripts making the rounds with my agent, I have one manuscript that is half way written, and one story in which I've got the first four chapters already completed.
Of course, if that publisher comes back and asks for a proposal for a couple of those pitches--well--I'd rather not think about that just yet. : )