A good warm up, with dynamic stretches and the performance
of drills which replicate the movements of your event in a controlled manor
are the best way to prepare for training and competition.
After exercise static stretches of the most used muscles will help return
them to the state they were before you used them.
If you don't have good flexibility then the occasional stand alone stretching
session will help to improve your range of movement as might disciplines
such as pilates and yoga.
If you don't have good mobility this can lead to a higher risk of injury when training or competing.