Let' say you tore a muscle. What should you do? Well, like anything, it depends on the details. If the tear is deep, and it burns when you even approach stretching it, take time off. Massage the muscles, or get a professional massage therapist to work on it. The Homeopathic remedy Arnica Montana (30x strength) is for sore muscles and bruises, and taken as directed, can help that muscle heal. You can also get Arnica gel at the Health Food store, and rub it directly on the area.
If the tear is tolerable, I will often do stretches around the area, to loosen up any tension on the affected muscle. So, let's say I tore my hamstring. When I stand and stretch, the pain is noticeable as tension, burning, and pain. I stop the exercise, and get down on the floor and do seated hamstring stretches. I will follow up with associated hip stretches, and some quad stretches. These do not hurt the affected muscle, but since they are opposing muscles to the torn hamstring, stretching them makes the hamstring feel better because there is less tension on it.
Oh, hot baths, saunas, and steams (like at your gym) help a lot too.