take it slow.
hang in the kiddie park and practice riding on to boxes.
if you are past that practice sliding the little boxes sideways.
then move on to the smaller rails.
you should be working on getting comfortable hitting jumps, making sure that you are coming off and landing correctly.
once you are confident with smaller features move to the big shit and try whatever you can get the balls to hit.
ask guys hitting tables if you can follow them to judge speed, make sure you carry enough speed onto the rails and boxes, and if all else fails ask one of the little rippers for some pointers.