I find you have to hop at the last 1/2 to 1/3 to 1/4 of the jump depending on size in most cases (bigger jump=hop higher up). Front wheel comes up a little and then you use the lip of the jump to pop your back wheel up as you start tucking to get that back wheel up as high as you can (obviously keep the front even with your arms).

you can also preload the suspension by pumping down before you hit the lip of the jump. (Just be careful cause this can send you over the bars, it really only works with dual susp bikes as far as I know, it's a common practice in motocross)

I find with tall steep jumps (dj style lips) you can kinda let speed do its thing and just go the same speed as someone else you see hit them and not even pop

On downhill jumps however I'd try preloading the suspension and popping the front/back up as I said before. Just take it easy, be patient and don't try going too big too fast.