To get this achievement you need to perform two special tricks in one jump.

Note: Of all the Special Tricks in the game, each riders unique stunt seems to last a about a second less than the standard stunts so your chances at this achievement are increased if you use Up on the Left Stick (LS) with both Left Bumper (LB) and Right Bumper (RB) first and then go straight into another stunt.

The best place to do this is on the second large jump on the Sandy Mountain track. Hit it with a bunch of boost and 100% pre-load while holding down both the LB and RB. Since you press Up on the LS to pre-load once you're in air you'll get your Special Trick right away. When it's near completion press the LS in another direction while still holding down the LB and RB to make another Special move.

It will also be very useful if you have an A Class bike with a high Trick rating. Level 2 shocks will be very helpful too.