Everyone has a slightly different method. I book them in order, starting with the earliest date first, because that day has already had bookings from guests who arrive before I do.
OP, if you can split up the task with someone, that's very helpful. My sister (who's my travel companion) and I split up the LLMP/SP duties by day, so we're able to attack it together. For a 4-day trip, it'd be super helpful to have this kind of help. If possible.
ETA: And . . . have your credit card and Disney password handy. Every once in a while even though I have a cc on file with Disney and I'm already logged into DME, they will ask for one or the other or sometimes both when I go to pay for the LLs.