all of the other answers are absolutely correct in pointing out the important of genetics as we all are differently endowed with the distribution of muscle fibers.
The thing that struck me, though, was that you do not specify for what to make people faster; 100 m dash or marathon. No two training regimens could be more different but the goal is to make the runner faster.
Another aspect is speed in sports. Training for tennis, for example, is very different from any running drills.
Muscle fiber makeup & genetics can be two contributing factors to someoAnesh speed. Also training such as sports specific training & speed & agility training can help in increasing someones speed. Exercises such as running exercises, leg exercises, training in an anaerobic heart rate zone such as sprinting exercises & running with weights can all increase your speed. http://www.personaltrainingbodybydesign.com/
Both Michael and Joanne are spot on if you ask me. The best athletes, no matter how hard they’ve trained over the years, generally owe a huge thank you to their parents for gifting them with such marvelous genes.
Do you incorporate some form of periodization into your training programs? It can be extremely useful for anyone looking to seriously increase their level of fitness (speed included) over time.
I’d recommend checking out the following link for some great HIIT workouts that (when used appropriately over time) will positively effect one’s speed: http://www.12minuteathlete.com/
Hope these help make you faster!