while moving, move the left analog stick away from the basket and at the time flick the shot button...if you are using an xbox360 controller it's the X button....this will make your player do a step back....you just have to follow it up with a jump shot by using the right analog stick or pressing the X button...
when going forward press the movement button in the opposite direction and 'shot' button at the same time. You will do a stepback, then just pull up a j :]