First of all when you say "popping", I am assuming that you mean ollieng(in other words using the board's flex to get more air. The best time to ollie off a jump is right at the lip(top edge of the takeoff). Too late and nothing happens, too early and you miss the "pop" that the lip gives you. There could be a few reasons as to why you are not getting much are: not enough speed, not a steep enough lip, popping too late or too early. Jumping is just going off the lip with both feet level, while "popping" is using an ollie motion to gain more air time off of the lip. In both cases, it is important to flex you knees in mid-air in order to absorb the shock of the landing. I hope that helps a little.