born fast?
Innate sprinting speed varies greatly from person to person. Some athletes, like Mark Lewis-Francis run the 100m close to 10 seconds flat as teenagers, while other less gifted contemporaries struggle to break 13 seconds over the same distance. It is a widespread, though not necessarily universal, belief among coaches and athletes that talent (in the modern guise of genetics) is the most important factor in determining sprint speed: athletes are born, not made. The well-known German coaches Jonath, Haag and Krempel state in their book Leichtatletiek I that female athletes reach their maximal base speed between their 17th and their 22nd, and male athletes between their 19th and 23rd. My personal experience, and that of a number of athletes I know personally, contradicts this, but then again I am no Ben Johnson. Be that as it may, given the constraints imposed on us by genetics, we can strive to maximalise whatever potential we have. This is my main focus.

individual differences
There are individual differences not only between athletes, but between the same athlete in different stages of development. Some athletes are naturally strong or fast, others are not. Some are "hardgainers", others gain strength easily. There is no one-size-fits-all training method.

laying the foundation
A beginning athlete first has to lay a foundation of general fitness and strength. In my opinion, healthy, reasonably fit athletes aiming to improve their sprint speed should embark on a strength and weight training program as early as possible. Starting athletes should follow a fully periodized yearly training schedule, beginning with general physical preparation (GPP), specialized physical preparation (SPP), and moving on to pure speedwork as track season commences. Technique is important in this phase, both on the track and in the gym. A variety of drills, and close attention to form, is essential.

building up speed
There is no simple demarcation between a "beginner" and "intermediate" or "advanced" athlete. There comes a period in an athlete's life, when following the classic annual periodization cycles of GPP in late fall and winter, SPP in early spring, and speedwork during the track season, will fail to produce the results it did in preceding years. The athlete will plateau: his times on the 60m and 100m will stagnate (although the 200m and 400m may still show improvement); his gym lifts will remain at the same level they were the preceding winter. Despite training as hard and as regularly as ever, the athlete will feel he is running a Red Queen's Race, "busting ass just to maintain". At this point, and possibly even earlier, it is time to drop the traditional routines and try something more "advanced".