start off small and progressively get bigger. its def not a trick you have to have massive air on. i first learned letting go with my front hand and eventually went to keeping both hands on and just moving the handle. its a fairly simple trick if you have solid ollies and surface 180s.
I would suggest riding switch and learning all the tricks you already know over again from that position. I wish someone had told me to do that, as I SUCK at riding switch! ;-D After that, start working on Grabs!