Cadence
Moving your legs fast is, to an extent, a genetic predisposition, however,
improvements can normally be made. Here it is a case of practice makes perfect,
the more you move your body fast the more you body gets used to it and the
faster you can move.
So, the most important thing to do is practice moving fast.
This can be done by just running fast.
Also, you can cut your stride length and do drills with quick movements, such
as high knees. The Event Specific Drills
performed quickly are good for this - particularly the heel flick, high knees drill.
Over speed running can be practiced as well. This can be done by the use
of a mechanical device to aid you eg. a high strength piece of elastic, or by
running on a slight downhill decline (no great than about 5 degrees).
Power
Much of sprinting fast is related to the amount of force or power that you
can produce. Other than the effects of running fast in training improving
the amount of power produced, much of this work is done in the gym and is
looked at under strength.
However, plyometrics are also important here - as these are
good a producing elastic power, as opposed to just strength which some gym
exercises, where slow movements are involved.