It is true what plummet says, when you've gained good speed and velocity, edge back upwind just before you think you're ready to go, also bend down a little more, leaning back to build up more pop, swiftly send the kite in the opposite direction of travel diagonally through the window, pop the bar and your body and you should be going up. If your not, just keep practising. Dont be impatient if you dont get it at first. And as your reaching the pinnacle of your jump redirect in the same way you were in the first place.
And if you follow these tips precisely you should get fairly decent hangtime especially on the FS