Further to Mark's comment,
You can also shake the back hand a bit to make the sail sheet in and out. It's not as vigorous as pumping and you can do it in the harness. It often does nothing except show you which sheeting angle will give you more power

More things to try:
* Search for a bit of chop to 'slide down' as you get planing
* Get your feet in the right position for the board for getting planing
(which means for a wave board stepping back slightly so you're on the flat part of the board)
* Use less downhaul and outhaul on your sail to make it bag out more
* Use a bigger fin
* Use a bigger sail
* Use a board with more volume (and more flat planing area)