if you are reffering to a wheelswap or front to back (whatever you want to call it :D ),
I find the more i compress my front wheel say on a rail, the more momenton i get to flick it to rear wheel,
Wheelswaps are quite an advanced technique, i ghess if you gap to front wheel you will get alot more momenton than if you endo then flick ur back end :D
I would try on two pallets, making a small gap, and going to front then to back,
just practice really, ive been riding 2 years this christmas, and i can just about wheelswap rails consistantly (depending on the size) at the moment i am consentrating on gapping to thin walls to wheelswap :P
cheers andy