To get as high as possible you just need to keep jumping.
As your confidence grows with each jump, you’ll gradually be able to control jumps that are higher and higher. When you want to start jumping really high, hunt down the biggest and smoothest wave you can, put on the after burners and hit the wave at it’s steepest point.
Stay sheeted in on the way up and you’ll continue to go up. When you feel you’re at the apex of the jump, sheet out and float down or sheet in harder and impress your mates.