This is something I'm really good at in Real Life, and not so good at in writing. Why? I'm guessing because each story I work on requires a certain depth of thought immersion. It's not easy to dip in lightly and then off to something else, at least not if I want to make progress. And of course I do! Also there's the idea that each project takes so very long that if you mix two or more of them, it'll take twice as long to get anywhere.
The only time I've tried two first drafts was about four years ago when I did NaNo for the first time. I hadn't finished my previous novel when NaNo started, so I dropped everything for the new novel (to officially participate in NaNo, you need to begin and write a novel you haven't previously started). At the end of November I had two partially completed novels and then spent several months alternating between the two to finish both first drafts. It was difficult and I vowed never to do it again.
Even playing with world-building or revising one while writing on another is difficult for me. All of these areas require a real depth of focus that makes it hard to shift gears from one to the other. I've been trying to learn how to do this better, especially in the last couple of years where I've been spending so much more time revising and therefore feeling stifled without the *rush* of creating that a first draft brings.
I started writing Tempest in July, thinking that once I got rolling on it, I'd pull out one of my older novels to revise. I tend to write in the mornings (my best time), then, the idea was, spend the afternoon on revising. I haven't started a revision project, though. Instead I started taking the Thinking Sideways class and bounced some new ideas around for that, then resurrected an old partial first draft--Dottie.
And now I'm finding myself doing the unthinkable and actually enjoying it: having two first drafts on the go at once. It helps, I think, that they're quite opposite stories. Tempest is fantasy set in a harsh environment. Dottie is contemporary women's fiction and quite humorous at times. So when I find that Tempest depresses me, I can switch gears and work on something fluffier.
This has been working well for the past couple weeks. I'm making steadier progress on Tempest and plan to keep it the higher priority until the draft is done. At this rate, that should be sometime in December, but if it takes longer, so be it.
I guess this means that I'm not revising anything more until next year. Two projects is ample to keep me out of trouble!