This will likely be one of the first achievements you get after completing the tutorial. To reach level 2, you need to get 500 XP points (going on memory - someone can confirm if it's different).
I found the easiest way to get this was to go straight into an Exploration stage, and simply drive about collecting coins and going over jumps, making sure to do tricks by holding a direction + X. Be sure to let go of X before you land or you will wipe out. Although to be honest, crashing also gives you XP, so you could still rank up.
When you've caused your avatar enough injury and racked up a load of points, press Start to pause the game and select "Exit Game" from the menu. Your XP summary will appear on the next screen, and if you've earned enough, the bar in the top right-hand corner will fill up and you'll increase in rank.
This will also come just through playing the game naturally, so no need to explicitly go and try to get this achievement.