I injured my shoulder falling off my bike last week. Should I ice or heat and/or stretch?

It depends. Your doctor can evaluate the injury to determine what the appropriate course of action is. Muscle strains or soreness generally respond better to heat, while ice is better for inflammation and bruising. A doctor can help you determine if there are any more serious injuries, like broken bones or tendon tears, so if you're concerned you should visit your physician. Wishing you a speedy recovery.
R.I.C.E. In the beginning use r.I.C.E. Rest, immobilization, cold, elevation. Later on may use hot compresses, ( or continue cold compresses if you feel better with that) use ointments for muscle pain. If you are not able to raise your arm see a dr.