Full keel boats are notorious for backing down poorly, although as Roger says, different boats do things differently. It's partly a factor of rudder design and placement relative to the prop; and whether the prop is offset or on the centerline.
Our schooner is full keel with a large, barn door-type rudder hung from the keel and a prop on the centerline. Prop walk is hard to starboard in reverse. We have to back into our slip (two pilings outboard, a bulkhead inboard and a very short fingerpier). As Kris suggests, we try to the extent possible to use the prop walk to our advantage. We approach the slip counterclockwise arc, genreally with the boat in neutral quite a ways out (we make a lot of way due to inertia) so that by the time we're about a boatlength away we're perpendicular to the slip and about 10' or so off the outboard pilings. Then we make a hard turn to port to line up with the slip, using bursts in forward in reverse to simultaneously stop the boat and pull the stern around. Then, as Roger says, it's short bursts in reverse, to get the boat moving backwards; alternating with neutral for steering control and the occasional burst in forward to counteract the prop walk. Generally we get about 1/3 of the way into the slip and then walk forward to the pilings, grab the bow lines and walk them forward to cleat them off. Then a couple of short bursts in reverse pull us back into the slip so we can get the stern lines. The bow line length keeps us off the bulkhead, even with the boat in reverse.
It's a dance, and it works about 50% of the time. Occasionally a crosswind will push the bow around and mess things up.
Experiment in open, calm water with your boat to see what it takes to back up in a straight line. You may find a method that allows you to back out, or you may find that, like others, it's best to walk the boat out to avoid dock-bumping. I'm pretty sure, with our boat, that I'd walk the boat out if I was backing out of the slip.
Mike Turner
Lazyjack 32 schooner "Mary'Lis"
Mobile Bay, Alabama