This is by far the hardest achievement in the game. The best level to attempt this on is Freestyle in New Orleans because of the large tabletop ramp in the center and the smaller ramps around the outside. Right off the bat, begin first with a Donut and a Cyclone. Next try to get a Wheelie, Sky Wheelie, and Slap Wheelie as fast as you can, use the tabletop in the center to try for a Sky Wheelie and Pogo at the same time. You should have 6 tricks by now, 7 if you've gotten a Big Save.
Now, use respawn to your advantage to put yourself in front of the center ramp. Aim for a Back Flip. The second you get the points for it respawn and go for a Flat Spin, repeat again and hit the ramp at an angle for a Barrel Roll. If you managed to get lucky and sneak a Big Save and Stoppie into the fray you should have 10 stunts by now. If not, use the smaller ramps along the outside to aim for a Stoppie and a Big Save. It helps to keep your Bonus Time, so if you're great at landing and controlling your truck then try to keep your Bonus Time. If not, don't worry about it and simply aim to throw in as many stunts as fast as you can.