Select the "Training" option from the main menu. Select any rider and board, 
and choose an easy trick from the list. Launch from the jump or from the side 
of the half pipe and execute the trick. Then, quickly press Right-C(2) while 
in mid-air. The trick list should re-appear. Select a trick that has not 
been unlocked, then resume and land successfully with the easy trick. 
The more difficult trick should now be unlocked from the list.