In the training section, turn your bike around and go the opposite direction from the starting point. You may go as far as needed so that when you turn back around, you will build enough speed shave seconds off the clock and complete the test within the time requirements.
On the number 3 training course in which you must follow a driver and be a few seconds behind for gold, keep driving right off the course until you see him smoke his tires. This will enable you to be right next to him or in front of him. On the first or second turn, if you ram your bike into his side from the inside of the track, knocking him to the outside, you can knock him off. Then, race to the end. If you are a decent driver, he may catch up with you at the end, but most likely you will only be a second behind and still get the gold.
In training, there are some challenges that have you go through the board with obstacles that you cannot touch or you will fail. On the same boards, you have time limits and you cannot go off course or you will fail. However, the time does not begin until you go a small distance in front of you. Instead of going forward, turn around and go the other way until you reach an obstacle in the road. Bump into it. If you are playing for the gold, which you should be in the first place, you have two seconds taken away from the little time you have. Ignore this, and just keep bumping into it until it does not take any more time away. Then, go back the way you were originally facing to start the challenge. When you go past the start mark, the clock will not change. You can now take as much time as needed to complete the challenge.