Starts are the most important to learn. Even 7 time champions often hover above the seat instead of putting all their weight on the seat. The goal here is to have as much weight on the front of the bike to keep it from looping out so sit on the font of the seat. Support the bike by staying light on your toes, too. Once you are in the best position for the start, meaning your elbows are out and head is over the bars (like doing a push-up), then you can pull in the clutch and put it in gear. I would start in 1st gear on a 125cc and 2nd gear on a 250cc depending on your weight and the conditions of the area you are riding in. Lighter riders and 4- stroke riders can usually get away with going up to the next gear. After all that, hold in the front brake and twist the throttle just about half way from the fully open position. If you have a starting gate or anything close to it would be helpful. When lined up you want a straight rock free line to work with. Looking to the gate next to you helps your reaction time for one reason, you can react faster when you are using you peripheral vision than if you are looking directly at an object. When the gate drops smoothly aply the throttle and clutch simultaneously don't just dump the clutch and pin it. Once in motion use your body to keep the bike perpendicular to the ground to get the best traction. If the bike begins to wheelie its not a bad thing. This means you are getting the best amount of traction. In this case you can arch your back towards the front of the bike to give it more weight. If that dosen't help the front end stay down then you can slip the clutch for a split second to bring the front end down. When I say slip the clutch, it means to pull the clutch in maybe an inch or so with out letting off the throttle so you don't lose engine RPM. After that its up to you to get to the first turn before everyone else. The best line is the inside becuase you can push riders towards the outside and take over their positionpractice starts religiously. Everyone has to learn to start before they can even begin.