You earn points by performing tricks. The score from consecutive tricks accumulates, as long as the time between them is short enough. Your total combo score consists of a base score and a multiplier, with your total score from the combo being your base score times the multiplier. All tricks contribute to the base score, but only back and front flips contribute to the multiplier, raising it by one for each complete flip. You need to earn a combo score of more than 10,000 points.
The best level to attempt this on is Insane Hills Level 6. Right at the start of the level there are a series of five or six jumps in which you can rack up enough score and spins on to reach 10,000 with no problem. Remember to jump before going off the jumps to give yourself more air time. Constantly being doing spins and grabs. Make sure to complete at least five different tricks to unlock the "Showoff" achievement. The achievements themselves do not unlock until you successfully end your combo by landing and stop doing the tricks.