Lets think what shoulders workout means. It means that you have to pump up their three different heads thoroughly. So you should use different exercises for each of those heads. These four movements work best for me. And it is very important to understand that for the maximum muscles growth each body part has to be trained not more than once a week.

Military press
This exercise works entire delts and is used to increase shoulders overall mass. First you have to warm up. Take a weight that allows you to complete 20 reps. Then perform 3 sets of 8-10 reps. This is a powerful exercise so you can use some forced reps at the end of the set.

Barbell front raises
This exercise provide a full feeling in the front delts and serves to reach definition of your delts. Use shoulder-width grip. Try to keep your body still. Move the bar slowly, concentrating on the front delts. 2 sets of 12-15 reps are sufficient.

Standing lateral dumbbell flyes
The following exercise is standard but despite of it it's number one for lateral deltoids mass and definition. After 8-10 reps of each set of the exercise completed in a good, slow, concentrated manner I advise to finish a set with 2-4 cheated reps. Work very hard on the negative portion of the rep. Never let the weight drop. 2 sets of 12 reps that's what you need.

Bent over dumbbell flyes
The best exercise for rear delts is descending sets of bent-over dumbbell flyes. Take a weight you can do 12 reps with. Then make 3 cheated reps. Without any rest drop down a weight and take new pair of dumbbells you able to do about 10 reps with. Continue to decrease a weight set by set doing 5-10 reps until your muscles give up. Rest about 2 minutes and make one more set, following the above mentioned technique.
You are probably going to ask me why should you use such a merciless method? Because you have to pump your delts full of blood. And especially your rear deltoids to make them look so exciting from the back poses.