Smash your shoulders when you get into the gym and eat right (5-6 meals a day, 1g of protein per pound of bodyweight as a minimum). I just finished putting together a split routine I want to start in the next two-three weeks.
Shoulder Day -
Dumbell Presses 4 sets 12, 10, 8, 6 reps
Dumbell Lateral Side Raises 3 sets 12, 10, 8 reps
Dumbel Front Lateral Raises 3 sets 12, 10, 8 reps
Dumbell Rear Lateral Raises 3 sets 12, 10, 8 reps
I'm also a very firm believer in switching things up. I alternate between dumbells and barbells a lot and revamp my workouts when I feel that my body is starting to get used to it.
Also compounds like deadlifts and rows will contribute to shoulder mass.