Enable the "Massive BMX bunny hops" code. Keep jumping very high by holding L for a long time. As you jump, do some flips (backwards or any funny stunt) and land perfectly. You will then receive a unique stunt award or an insane stunt award and your skill will increase. To do this perfectly without falling while doing the stunts, use the "Never fall off your bike" glitch. Get some speed, jump as high as possible, do stunts, and do not fall. This will increase CJ's bike skill.