I'm contemplating going back to an earlier project. Not, heaven forbid, re-working the text, but writing a new text built on the same ideas and situations. And one of the advantages of doing things this way is that the researched material has mulched down nicely in the back of my head, in the sense I was discussing here. The stuff you found out needs to become stuff you just know, so that there's no longer any difference between them: all compost. But is there anything you do to hurry the process of mulching down? Are there compost accelerators?
I think there probably are, although as a killer of spider-plants I'm not the best person to pursue horticultural analogies. But I do know that making compost is a mixture of turning it over, and leaving it be, and maybe that's true of writerly compost to. So what might you do, to leave things be?
Ignore the project, and wait for it to claim your attention again. Not-thinking, if you like. The character, the situation, the period which won't go away, is almost always one worth having another go at (as I was saying in The Value of Forgetting). But to be sure it is that kind of character, you need to walk away from it. When you do let it reclaim you, you'll have picked up all sorts of other things which change and enrich the possibilities.
Write something else. This is the quicker way to push a project out of the forefront of your mind, so that it can get on with breaking down, and is one reason I'm positively pleased to have two projects, at different stages: getting on with the other one is actually helping this one too.
Be patient. If you turn compost over it too often it cools before the separate elements can mulch together, but if you're someone who deals with desire by going headlong for it, you may read your impatience as frustration. But frustration, at bottom, is a kind of fear - in this case that if you don't grab the project - ideas, characters - now, they'll somehow escape. But the nice thing about writing ideas is that they're just as good years from now, unless in 2009 you had a great thriller idea set at the London Olympics ... in which case you'd better get on with it. But for anything else? Be patient. Apart from anything, the longer you leave it the better a writer you'll be by the time you get there.
And one way of dealing with the urge to go headlong is to let yourself do some turning-over. Not, I'd suggest, as part of a time-tabled progression towards the moment when you start drafting the novel, but in a looser and more free-form way that encourages stuff to "rise into the anarchic, gift-conjuring" part of your mind. So what kinds of turning over might you do?
Reading round. In reading non-fiction at this stage I avoid making notes: this is all about feeding the compost, not about providing a traceable bio-chemical analysis later. Notes help you to remember, but they also pre-determine what you will remember. If it's my own copy I might write headings in the margin, though, so I can flip through later to confirm what I've remembered or make notes in full. In reading fiction it's much the same. I absorb, notice mentally perhaps and, as when I was reading Wolf Hall, trust that my intuitions about storytelling are being fed and grown. Another kind of reading would be things like poetry, myths or folk tales around the themes you think you might be working with. I might keep a list of what I'd read, but not more.
Dreaming on Paper. As I was discussing here, the kind of thinking-on-paper which you could call planning, can actually be a way of doing some much more free-form but focussed imagining. In a workshop we listed all the different things you might do: free-writing, family trees, sketch-maps, spider-diagrams of tensions and relationships, plans of buildings, clusters on characters or images or themes, rhymewells on important words, lists of names, collecting quotations that seem to resonated, jotting down possible titles if they occur to you. Then there are the things which are slightly nearer to actually writing: pen-portraits of places and characters, or even a short story that brings someone or something into focus, or catches a voice. (If you do anything else by way of dreaming, not planning, then do mention it in the comments.)
Brooding on the story, not the plot. That is, on the journey you make, not the route you take. Again, this needs to be very free-form - very much dreaming, not building. I try - though I don't always manage - not to let myself be lured into beginning to work it out in an organised, logically connected way.
And if I really can't help myself - if it all seems to so ready I really must start planning my route - my plot - or die, then I let it. As with your characters, so with your stories: you're in control, but sometimes you have to hear what they're telling you, and do it.