What Windxtasy said; pull the sail parallel to the water and only start lifting up when the clew is clear, I find keeping the arm extended and swimming upwind really helps.
If youre starting close to the tip, same technique, get the sail airborne then handwalk your way down the mast till you get to the boom.
If you do have to swim the sail through the water to get it around to the right position to waterstart, grab it up close to the tip and tow it round mast first, I often find once the sail is across the wind all that needs doing is to give the sail a little bit of elevation at the tip whilst still towing it forward and the whole sail will fly free.
I think I spent a lot more time than most swimming round my board and sail trying to figure the waterstart out, looking like a half drowned seal. Lucky me no learn in open ocean with all the grey-suits swimming round
