What can I do to rehab my arm/shoulder to maximize strength and functionality?

Cuff Strengthening. The best place to start is rotator cuff strengthening. The rotator cuff is the core of the shoulder. If you are early in your surgical recovery, check with your surgeon before embarking on a strengthening program.
Physcial therapy. The best way to maximize function and strength of the arm/shoulder is with a physical therapy program. Your physican should evaluate you to determine the nature of the problem to see if it is muscle, joint, tendon or bone related. They can then refer you to a physical therapist who should work with you to develop an appropriate exercise program.