Novels, novels, everywhere... I'm working on about three at the moment, although it may be two again after my attempts to play around with my own the other night.
Sometimes people ask me how I keep everything distinct in my head when I happen to have more than one thing running at once. The answer is complicated. Partly, it's because I don't try to do it all in my head: I'm relying on carefully written plans/outlines to give me the shape.
Partly, it's because characters in books are closer to one another than most people admit. We see so little of them, and in such a controlled way, that creating differences between them is relatively straightforward. Particularly if you happen to view them as a part of the story as a whole rather than separate individuals, because that helps to give each one some of the flavour of the story.
Partly, it's an organisational thing. I tend to work on particular pieces at different times of the day (or at least in a consistent order) so I know which space my head has to be in for each one.
On a separate note I may just have given up on the idea of complete spontenaity for novels. Pantsing through the current idea has been giving me some nice ideas, but I just realised I have no idea where it is going.