It sounds like you are inexperienced with track and field. I would recommend finding a coach to teach you the fundamentals of sprinting. Working the basics of technique will give you the biggest gains in the shortest amount of time.
Besides technique, you obiously need a great strength/weight ratio, strong compliant and plyometric tendons in your lower legs, flexibility, strength, and speed throughout the entire range of motion, and (particularly for the 200m) strength endurance.
Might as well start practicing now.