Around here if the wind is light it's very shifty. Being in the right wind (and trimmed for that wind) is far more important than boat set-up. I find that just reacting quickly to a wind shift will often get you a few boat lengths on the competition.

I rarely raise a board in light air. I figure that when you are going slow you need all the lift you can get. Also if you are constantly changing points of sail, the disruption from moving about and futzing with the board will cancel out the decrease in drag. I don't raise a rudder either.

MauganN20's points about getting your weight forward, not disturbing the boat by moving about and being light on the helm are also very important.

Finally, to compete well in light air you have to practice in light air. Not many people have the patience to do that. But those that do are almost always at the front of the pack when the wind shuts off, dispite all the griping about "unfair conditions".