Set the preload so the fork sags about 20% of the fork's total travel, center out the rebound adjuster and go ride. Adjust rebound to feel.
Too little rebound will make the front end wallow and feel loose, too much won't let the fork extend, resulting in a harsh ride and nervous handling.
with the preload part, do you mean with your weight on it? IF so, in an upright position> or in a more aggresive position?