If you are feeling weak in your shoulders I suggest the following exercises. The first set actually deals with strengthening you scapular stabilizers (the base of all shoulder movements) first then working in the rotator cuff. The exercises are listed below:
1. Scapular Stabilization exercises-“Prone 6”- You can perform this exercise by lying prone or on your stomach in six (6) different positions. The first position is like what is described above, arms out at your side forming a "T" with your palms facing downwards, hold this position for six (6) seconds. The second position is the "T" but with your thumbs facing upwards. The third position is forming a "Y" with your arms, palms facing downwards. The fourth position is a "Y" with your thumbs facing upwards. The fifth position is with your shoulder and elbows at 90 degrees or basically making a field goal. The sixth and final position is with your arms next to your side attempting to touch your elbows together with your palms facing the table. You should hold each position for six (6 seconds) completing each position three times. You can increase the difficulty by first increasing the time for each hold, then progressing to adding cuff weights or performing the exercise on a physioball. The first time you complete this exercise you should have someone watch you because a common technique error is by using your upper trapezius (or shrugging) to stabilize your arms.
2. Rotator Cuff Exercises-Standing flexion, scaption, abduction, and side–lying external rotation. To perform these exercises start by standing up with your arms next to your side. Pinch your scapula (shoulder blades) together and raise your arms no higher than your shoulders. I would start with no weight then progress in 2# increments, 2 sets of 15. To perform scaption you start the same as the flexion but this time raise your arms at a 45 degree angle. To perform abduction you begin the same as the previous two exercises but raise your arms straight out to your side. Finally to perform side-lying external rotation lay on the side opposite of the shoulder you want to work on. Place a small rolled up towel under your arm with your hand resting on your stomach. Then rotate your arm so that your hand is goes out to about 45 degrees.