First you must unlock the "Collateral Damage" Event, unlocked at 50 total single player career medals.
Select "Archipelago" (the first track). The best option for this is the Scorpion 450cc bike that you will have unlocked. It is possible with the other bikes, and some might find it easier with the Phoenix 250cc.
Either way, start the track, and I recommend completing it at least once or twice to know what's coming up. The track is about 45-50 seconds long.
Now it's time to aim for the achievement. At the start of the race, just hold down your accelerator and make sure not to let it go. Steer your bike to make sure you don't fault. Note: You are welcome to feather the brake (while still keeping RT fully pressed) to slow down, or to stop your tire in the air, letting you go a little slower if needed. When landing, make sure to land on your back tire, at about a 20 degree angle to the ground, as this will make sure you don't flip and let you continue with speed even if you overshoot the jump. You may encounter 1 or 2 troubles along the way, but you can always revisit this track later on when you are more comfortable with the game.
View the video for my personal run and guide of this achievement: