Also, try to use a bit of crop as a ramp. This will also increase height in the jump.
Don't forget your landing! Bringing the kite forward as you descend will give forward momentum so that you don't just plop down in the water.
Point your board down wind on landing. I'll repeat this for emphasis.
Point your board down wind on landing.
A smooth landing is as important as a high jump. It's all about style.

And if it all goes pear shaped and you've over rotated and are heading for a painful entrance into the drink, ditch the board to save serious injuries.
Most injuries on the water I
personally know of have come from jumps. (knee dislocation, ankle fracture, heel shatter, dislocated femur, dislocated shoulder, fractured ribs, concussion, retinal detatchment, lacerations)