I just bring my energy up more, squeeze just a little, put my hand forward and off we go!

But if that doesn't work for your horse then just try bringing your energy up, squeezing just a little, kiss or cluck, and if he still doesn't go into it take a rope and swing it across your shoulders first and then let it get longer and gradually spank him on the butt, but not hard. Also, when a horse gallops, his weight shifts primarily to the forehand so it's okay to lean forward just a little bit.