In reply to Oogachooga:
The art of redpointing is really the art of remembering. Work out how to do the moves and then remember them for the redpoint.
On an easier project you might only need to remember the hand sequence of the crux. If it's a bit harder for you'll probably need the foot moves too. Harder still and knowing the moves into the crux will help by arriving at the crux fresher. On something near your physical limit, typically 3 -4 grades above your onsight, you'll probably want to know all the moves, where to clip from, all the foot placements, subtleties of body position, tempo, where you can get the slightest rest, where to chalk up etc.
Remembering moves can be quite hard at first, especially if you've done mostly onsighting before. Going over sequences in your head can help. Writing them down can help too or even making a 'move topo'.
Once you think you know enough to possibly do the route you can start having redpoint goes. If you fall, take a hang, analyze why you fell, and maybe rework where you fell or any other bits you think you could do better and try again.
Another part of the difficulty is knowing how much or how little to work a route. The more you work it the more tired you'll be for redpointing so you want to practice it just enough, but not too much. I don't think there's any simple formula for that. The more you do the more experienced you'll become.
On routes near your physical limit, redpointing becomes really interesting. When you know every move inside out and you're still failing you have to figure small subtle differences and things you can do better. And executing a whole route perfectly is not easy, there are so many small mistakes you can make. It becomes a real mental challenge.