Stretching, for an athlete, is just as essential as base mileage and good nutrition. It is one of the cornerstones of healthy training, and yet it is often one that runners overlook. Head out to park on a Saturday morning and you will find runners with one heel up on a bench, trying to touch their toes. They repeat the process on the other side and then tear off for their run, heedless to the problems that they could be inviting. Lack of flexibility can be a significant factor leading to injury and carving out ten to twenty minutes for a good stretch each day will pay serious dividends.
Before you head out, try some basic moves, to get yourself warmed up. These stretches (known as dynamic flexibility) mimic the running motion and get your body ready to run. Start with hip swings and arm circles to get your major muscles warm; 10 to 12 repetitions on each side will work well. Then, try a few, slow walking lunges to open up your hips. Finish off with 10-12 calf raises and you will be ready to run.
Post-run, give yourself at least 10 -15 minutes to stretch. Make sure you incorporate stretches for your hamstrings, quads, hip flexors, IT band, calves and lower back. Check out this link for great videos and how to guides. The time you spend on this will not be wasted. Flexible muscles are strong muscles!