I believe that distance running/walking engages various systems in our bodies that connect us directly to our roots. Primitive man had to walk and run for survival - thousands of miles a year. Through millions of years of evolution, the muscles, tendons, bones, energy systems and cardiovascular components adapted and expanded the capacity of the human body to cover long distances. Over this extended period, a series of psychological rewards also developed. This is why we feel good when we run and walk at the correct (conservative) pace for us.
Get a doctor who knows running and stay in touch with him or her. Getting a good diagnosis can speed the treatment and get you back on the roads quicker.
Don't stretch the area until it heals (unless you've injured the I-T band-ask your doctor).
Stop activity that could possibly use the injured site for at least one to two days. In most cases your doctor will tell you that the injury doesn't have to heal completely before you run again, but you must get the healing started and continue a program that doesn't re-injure it. Again, talk to the Doc.
Ice! If the injury site is near the surface of the body, ice massage will usually help. Be sure to use a chunk of ice and rub it directly on the injured area until it is numb (usually 10 to 12 minutes). Be sure to ice at the first sign of injury, ice as soon as possible after exercise, and keep icing for at least a week after the pain goes away. The regularity of the ice treatment is very important so do it every day!
Compression will help to restrain further inflammation. Wrapping a sprained ankle after injury will reduce the inflammation. This is another area where your running-oriented physician should advise you.
Elevation can help to reduce inflammation.
Massage can dramatically speed up the healing of muscle injuries. A massage therapist or physical therapist, who is experienced in working with runners, should be able to advise you 1) whether your injury will heal quicker with massage and 2) when it's time to work on it (immediately after injury is not usually a good time).