On modern boats (e.g. F18 or N20) a bunch of downhaul to open up the top of the sail and allow more sheet tension that running minimal downhaul is faster in the really light stuff. (Flat sails - like Wouter said).

Plus what has already been said - weight up front, move gently, be smooth, keep in the groove, don't give up.

Another good move is to watch the puffs coming down the lake carefully and get in the right place at the right time, and when going down wind, if you are in a puff, gybe to stay in it.

Chris.