After finishing the first draft of a book, I like to leave it for around a month because I find it easier to spot flaws when it comes to the second draft. Instead of sitting on my bum doing nothing (which I did not do over Christmas*), I'm starting to plan my next book - unsurprisingly now refered to as Book 4 (although it does have an actual title).
I planned the hell out of Book 3, right down to each chapter and I found it really helped me. Not only could I spot major flaws as I planned it and prevented any ball-achingly major changes before I started writing it (something I wished I'd learned before Books 1 and 2), it was also a comfort knowing exactly what I had to write each time I sat down at the computer. It wasn't a perfect process. I still sat there twiddling my thumbs and browsing ebay at times but it did help. So much so I'm going to plan the hell out of this book as well.
I already know the story quite well as I tried to write it a few years ago. I loved the story, one character in particular, but I got stuck on the plot part way through and gave up (I gave up a lot back then). I remember thinking I should have planned it better (or at least planned a little as I didn't really plan at all until recently) but I didn't have the heart to unravel what I had and start again. But the story stayed with me and so I'm going to try again - but better planned this time!
I haven't done much planning yet as I only started on Monday but it's fun getting to know a brand new set of characters. Plotting and building up characters and families is my favourite part of writing.
*whoa, what the hell's going on with my nose. Is it getting bigger? Feck, it is. I look like bloody Pinocchio!