How to avoid injury while doing exercise/sports ? (ST2U.com)

I found that , most of the people getting hurt while they doing sports, through my many years experience of sports, i found that most of the people never do warming-up or stretching their body before their's sports/exercise. This is not right, because it will affect the future development of the bone.They should slowly cumulative the amount of exercise/sports , or slowly increase muscular endurance. Main notes :
1) Do stretching or warm-up before doing any exercise or sports.
2) Step-by-step exercise or sports.