Developing The Delts
The deltoids are an important muscle group that work in conjunction with the back, shoulders, and pectorals. They are a small muscle group and therefore they grow more slowly. Training them is a long term goal that requires patience, strict form, and more patience. The trapezius muscles (traps) are also key in developing the delts and are also difficult to isolate and train individually. There are many excercises that help specifically build up the delts and traps, but they can also be trained during your normal lifting routine. The posterior delts are the least targeted during regular training so if you want to develop the delts, make sure you focus on this area.