As a foil board is way heavier than a normal windsurf board, slipping out of the footstraps during a jump is more likely. Therefore, make sure your footstraps are tight and your feet are all the way inside to provide you with enough grip during the jump.
To obtain a lofty takeoff and decent airtime, you have to build up enough pressure on the foil by following the pumping movement. Just before the board is about to touch the water, lean back aggressively to generate the maximum amount of Lift.
Sheet in the sail during takeoff and tuck your legs underneath yourself just like doing a normal jump on a windsurf board. This will make you stay composed in the air.
Focus on the landing and stretch your feet just before touching the water to absorb the pressure and obtain a soft landing. After that, push the foil on the plane and keep on gliding.