Dynamic Stretching should be part of your warm up and should simulate the activity you are about to perform. You will find a list of dynamic stretches at your gym or online here which you can add to your programme. This prepares the body in a far more effective manner for the exercise you are about to perform. These type of stretches need to be performed after the warm up and should be done at a warm up to exercise pace which ensures the heart beat stays elevated which is an important part of any warm up.