Keep your body as far forward...
Keep your body as far forward and as low as possible, keeping as much weight as you can on the front end to reduce the chances of a wheelie.
A good start is an essential part of a sprint race and practically the whole race at the dragstrip, making it important that racers at both venues master the art of a good launch. The trouble is that with just a handful of passes at a drag meet or a couple of sprints at a club event, practice is a bit hard to come by. There is a lot of action packed in just a couple of seconds of time, and whatever you can do to get to the strip regularly will pay off in better technique, for roadracers and dragracers alike.
A good launch begins well before the flag drops or the lights illuminate. The desired goal is to leave the line accelerating as hard as possible, and to do that you'll have to manage the throttle and clutch effectively to limit wheelspin and stop the front wheel from rising off the ground. Ideally, you want to deliver just enough power to the rear wheel so that your bike is on the verge of wheelspin or a wheelie, right from the nanosecond the light turns green. In your everyday riding you should become comfortable with slipping the clutch from a stop, and modulating both the clutch and the throttle as the bike accelerates. The more familiar you are with how your bike reacts under these conditions, the easier and more natural it will be for you to manipulate the controls properly without actually having to think about it.
To reduce the chances of a wheelie, position your body as low and as far forward as possible, keeping your upper body as low to the tank as you can. Note that wheelies have a snowball effect: the more the wheel comes up, the easier it is for it to come up even more. It's best to not let the wheel come up more than a couple of inches if at all, and the quicker you can get things under control the better.
Avoid the temptation to watch...
Avoid the temptation to watch other competitors for your cue. Concentrate on what you're doing, watching the flag or lights for the start, then minding your engine rpm as you leave the line.
Dragracers constantly refer to a "launch rpm", and you'll need to find the best engine speed for your bike to properly leave the line. Remember, you want just enough power to be on the verge of wheelspin or a wheelie; for a big bike such as a Hayabusa or ZX-14, you'll need just a few thousand rpm showing on the tachometer. A high-revving middleweight like an R6 will need 10,000 rpm or even more for a clean launch. Pick a launch rpm, and have your engine spinning at that rpm a couple of seconds before the start. Avoid blipping the throttle and racing the engine; keep a steady throttle hand and the revs constant at your chosen launch rpm.
At the dragstrip, a street tree illuminates the three yellow lights in 0.5-second intervals and the green another half-second later. A pro tree illuminates all the yellow lights at once, then the green 0.4 seconds after. A perfect human reaction time is about 0.4 seconds, so on a street tree you want to leave just after the final yellow light; on a pro tree, go when the three yellows illuminate. Don't watch for the green light, as you'll be too late; keep an eye on the bottom yellow light for your signal to go. Roadraces may begin with either a flag or light, and it's best to check out a few races before your own to see how your particular club's starter operates. For lights all you can do is watch the light itself, but on a flag start, watch the starter for a tell-tale such as the tip of the flag moving, the starter's elbow bending or the like.