Foam rolling should be added to everyone's stretching/cool down routine, or even just implemented into your every day life. It's a great way to release some of the trigger points before you stretch out the muscle.
Think of a trigger point in your muscle as a knot tied in a rubber band. If you pull the two ends of the rubber band without taking the knot out, the knot just gets pulled tighter, which is the same with a trigger point in a muscle. Foam rolling works on the trigger points in your body before you lengthen your muscles through stretching.
See the picture below for some how-to's on foam rolling.