Here is a movement to use to help warm up your shoulders.
Lay down in a prone position (face down). Place a PVC pipe behind your neck and press toward the ceiling. Maintain the pressure in an upward fashion and perform an overhead press. Perform 10- 15 reps prior to doing any overhead movement. As this becomes easier you can add small change weight plates onto the pvc pipe. Give these a try but be aware they are harder than they seem.