The best time to stretch is immediately before and after aerobic activity. Before stretching, take a few minutes to warm up as stretching cold muscles can cause injury.
Flexible muscles are less likely to be strained or pulled than tight ones.
The best way to guarantee yourself an injury is to try to lift more weight than your muscles can handle. Gradual, progressive resistance is a far more effective and safe way to increase muscle strength. Not warming up prior to aerobic activity Muscles need time to adjust to the new demands aerobic activity places on them. Rather than hitting the treadmill running, for example, take a few minutes to walk, build up to a light jog, and then hit your stride. Too many people wrap up their workouts and head straight to the showers.