Anyone who is participating in physical activity should be performing some leg stretch exercises regularly after they finish. This is even more important for runners in particular as they often develop very tight quads, hip flexors and hamstrings after going for a long run or a sprint session.
The first leg stretch to perform is for your quad and should be completed by standing on one leg and then bending the other at the knee and grabbing the ankle with your free hand. Ensuring that your hips are forward (think of squeezing the bum to accomplish this), gently pull the leg in the backwards direction. If you mentally imagine trying to draw a line with your knee, starting from right below your hips backwards you will accomplish the exact movement you are looking for.
The next leg stretch to perform is great for your hamstring muscles and is a simple toe touch. This can be done either sitting on the floor or standing straight up; whichever is your preference. Try and keep the knees straight while doing this, however do not lock them.
Finally, finish up with an exercise that will lengthen the calf muscle. To do this one either stand so you are facing a wall or stand so that your heels are just hanging off a step. If you choose the wall method, you want to prop one of your feet up against the wall and then slowly lean inwards. Hold this position and then relax and repeat again. If you are doing it on the stairs, all you need to do is hang off them so your body weight works with gravity to create a pull on the calf muscle. You can also do this one leg at a time if you prefer.
If you are particularly sore, after doing these exercises you should also consider taking a nice hot bath. Sometimes that is one of the best methods for reducing muscle soreness and fatigue.