The resistance band is the shoulder muscles best friend, there are so many different exercises that you can perform, due to the many movements that the shoulder joint can make and the adaptability of the resistance band.
X country skiing shows how you can work not only your shoulder muscles, but also your heart and lungs. It provides a good workout, especially if working at a smooth controlled speed.
Stand with your front foot placed centrally on the resistance band, with your rear foot one stride back, so that you have to lean forward slightly.
Holding a handle in each hand, raise one hand up to shoulder height (straight arm) in front of you, whilst taking the other arm straight behind you.
Work the arms in an alternate arm fashion, holding in the upper phase for a split second.
Focus on keeping the movement smooth, using the muscles of your shoulder to lift the bands up and back, rather than those of your legs, or twisting from your abdominals.
Aim to gradually build up the length of time you can perform the exercise, keeping the movement fluent, try and aim for 20 - 30 seconds with a similar time of rest before repeating again. As you get fitter, either increase the time, make the band harder, or simply repeat 3 times plus.