It really depends on what I have knocking around my head, what people ask me for, and what seems urgent to me. There are times when I'm happily just writing a short story at a time, finish one and take a break, then start another.
Right now, I have my main novel, I have a secondary novel, I have a series of comic book scripts, and the content-work for a video game.
But strictly novel-wise, I tend to crash my way through the first half of a novel, and then putter out (the second half is the most work, a short story writer by nature the length begins to wear on me). When I putter out, I shift gears and explode into a second novel, halfway through again. Then, I bounce back and forth whenever I have something useful to ply to either one.
I think as long as you're writing and keeping busy, you're fine. I think if you're writing more than one project, though, you might look into getting Mountain Dew fed directly into your heart, though. I have a lovely injection tube running into me right now. I'm a neon-yellow Borg.
