Use wax, not soap. A candle is fine... And make sure you have a decent-quality screwdriver that matches the slots in the head of the screw. Good screwdrivers, rather than the potmetal bargain sets, really help*. If you look at the tip of a phillips-head screwdriver and it's already gacked, throw it away (or give it back to the gacker :evil4

. I find it's easiest to run a screw in and out of the holes to cut the threads first, with the neck laying on a towel and me concentrating on the screwdriver. Instead of trying to cut the threads & hold the neck at the same time. You're asking questions - that's a good start.
*(Everything about lubrication, pilot holes & screwdrivers that FIT goes quadruple when it comes to the bitty screws - ESPECIALLY the tuner-location screws. They don't need to hold anything on, they're just alignment pins. So there, making the pilot holes big is a great idea. Search "tuner screws" here for some Steven King-surpassing horror reading sometime.)
ADDENDUM: I have seen at least four different "#8 screws" that differ in sizes slightly, and I think it's a good idea to use new screws on each neck and keep the old ones with the right neck. Otherwise, at some point the statistical inevitability will hit - you'll try to remount a neck threaded with fat #8's using skinny #8's. heh.