Work on your bunny hops and j hops you will eventually figure out the timing and it will help you go higher. As for tailwhips you can try it off a ramp if your not able to get hight. Also on your free time practice spinning the deck continuously it will help you tremendously.

if you jump off of a curb high and then kick your feet and flick your hands at the same time. make sure to just try jumping regularly to get the height