Have you ever been to a posh dinner and been presented with a vast array of silverware spreading in ranks either side of your plate? Re-writing is like dealing with all those forks and spoons without getting it wrong and spilling soup down your front, or using the butter-knife to eat your peas. The simple answer is to start from the outside and work your way in.
I'm a BIG fan of rewrites. I think the quality of the rewrites is the difference between getting published or not getting published. (I can hear the planners clattering away at their keyboards about to lay into me for wasting time and not being efficient enough to do a decent piece of work first time round but hey - this is my blog, right, and what I say goes.)
The first thing to do is put the book away for as long as you can manage. The longer you leave it, the more distance you have. The more distance you have, the more you read like a disinterested reader, and the more you're able to spot problems. There's what you think you wrote and there's what you actually wrote, and if you're too close you can't see if there's a gap.
When I did this on my first novel the gap was about four months, mainly because I was incensed that the world hadn't realised what a startling work of genius had just landed on their doorstep and turned it down. Cue metaphorical flouncing out of the room and mega sulks from me. When I did finally go back I was ready to concede that the world might have a point.
So imagine spreading your starched linen napkin across your lap, gearing up for the lovely meal ahead. You've been thinking about it for ages, you've got various ideas as to what you might expect to see but you're open to whatever turns up on your plate. You know it's going to take time to get through all the courses and you're ready for that. Psychologically you're prepared for it to take as long as it needs. Ready? First course coming up...