For a discussion of stretching, read my stretching page. Remember the cardinal rule of stretching: You should feel no pain, that is, don't stretch so hard that you injure yourself! It's OK to feel stiffness while you stretch, but not pain as in "injury". When you stretch, hold each position for 10 - 20 seconds and then relax. Repeat as many times as you'd like. However, don't do a lot of stretching before a race, because the stretching will sap your strength. Be gentle with your muscles if you stretch before you run, because your muscles are cold.
Note: One stretch that I do is not illustrated in this page. The stretch is called the "furniture lift". With your runningshoes on, place your toe under the edge of a sofa or heavy chair and lift up with your toe as if you were attempting to move the furniture. The purpose is not to actually move the furniture but to put stress on your shins. Hold the stress for 10-20 seconds and then relax. Repeat using the other toe, and repeat the sequence several times.