A proper warm up gives your muscles and joints a chance to loosen up and prepare your body for a more strenuous activity. Do dynamic stretches with controlled leg movements before working out to loosen up and improve your range of motion. You can do leg swings, skipping drills, backward jogging, high knees, butt kicks, walking on toes and heels as part of the warmup. Running strides are also beneficial to do during the warmup or as they will recruit your fast-twitch muscle fibers and boost your blood flow to your muscles. Strides are accelerations of around 100 meters where you start out easy and build into an effort upwards of 95% of your max speed, and then gradually slow to a stop. Look for 3-4 sets of 20 -30 seconds per stride and 60-90 seconds rest between each one. Strides can be done following a run to shakeout some of the tightness you might feel after running at the same pace. The cool down will safely get your body and muscles back down to normal operating temperatures.