Start of in pow just (like mentioned above) do the beachballthrowing movement, kick your feet back, tuck as hard as you can, dont keep your knees together (2reasons, for a better tuck and you wont get a knee tot the face if you land)and try spotting your landing, this aint easy becaues youre tucked and inverted, but try spottin it as soon as possible.
in the beginning you probably wont be throwing them of anything huge so be sure to keep tucked longer than you think and everything will be fine
Oh and you might also wanna try them first without skis, just jump of something steep-powderish with your shoes, (a roadside or something) and just tuck tuck tuck (and keep your knees apart)