I know few things would be cornier than to start this section up with the phrase ”shoulders are probably the most important of all muscle-groups”, however the reality is that they just are.
Over the ages, the classical V-shaped upper body with wide shoulders and a narrow midsection proved to be the ideal look physical culturists strived for. I suppose there’s no need to iterate the importance of well developed shoulder muscles in achieving this look.
The muscle-groups that will define the general look of the shoulders and thus the upper body are the deltoids and the trapezius.
The deltoid is a three-headed thick muscle linking the clavicula and the scapula to the upper arm. It’s functions include lifting the arm (front and rear deltoids lift the arm to the front and back respectively, side deltoids to the sides) and rotating it.
The trapezius is a flat muscle - also triangular - and it makes the connection between the neck and the shoulder blades. These are the muscles that lift your shoulders when you shrug, and they also participate in every frontal lifting motion. (frontal as in lifting something in front of your body and not above the head)
Famous bodybuilders renowned for their excellent shoulder development are Kevin Levrone, Nasser El Sonbaty, Dave Draper, Frank Zane. These guys are characterized by the ideal square look in their shoulders. Bodybuilders who exhibit a well developed yet sloping trapezius tend to have more of a hanging look in their shoulders, which makes the appearance of the upper body less spectacular in certain poses.
Another thing that every bodybuilder should acknowledge is that shoulder width and trapezius thickness are two different things. Shoulder width is greatly influenced by the underlying bone structure, which - in turn - is a result of genetics, and as such cannot be in any way modified. Examples in this sense would be Reg Park, whose relatively narrow shoulders have been practically saved by the great development in the deltoids he achieved.
Dave Draper is the other side of the coin, as his not-too-bulky deltoids were wonderfully complemented by the great bone structure mother-nature endowed him with.
But enough about general considerations regarding the muscles of the shoulder. Let’s get down and look into what we all came here to see: shoulder exercises.
Let’s look at training the deltoids first.
There are basically two ways to approach deltoid exercises: power and isolation. Power exercises are all about presses. Because of the fact that - in these exercises -one starts out with the arms bent and the weight above shoulder-level the triceps gets involved as well as the deltoids. Thus, these exercises can be done with considerable loads, a fact which makes them power exercises. Deltoids react very well to heavy workloads, it is why placing a lot of accent on Shoulder Presses can pay huge dividends when it comes to deltoid thickness.
Raises are needed to thoroughly isolate the different heads of the deltoids, and, through this, to achieve the right deltoid definition.
These raises can be lateral, front or rear raises, each of these exercises working the corresponding part of the deltoids.
Because they are isolation exercises, the amount of weight one can use is rather limited. The goal of Raises is to achieve definition rather than muscular bulk.

Shoulder exercises:

PRESSES:

1) Shoulder presses executed behind the neck
2) Shoulder presses executed in the front (military style)
3) Dumbbell shoulder presses
4) Shoulder presses a.k.a Arnold press
5) The clean and press exercise
6) Shoulder presses using a machine
7) Behind the neck presses with cheating (standing)

RAISES:

8) Lateral raises while standing
9) Cross cable lateral raises with one arm
10) Side cable lateral raises with one arm
11) Cross cable lateral raises while seated (with one arm)
12) Dumbbell laterals with palms turned outwards (standing)
13) Lateral raises using a machine
14) Frontal raises using two dumbbells
15) Lateral raises executed with two dumbbells leaning forward while seated
16) Lateral raises executed with two dumbbells leaning forward while standing
17) Cable laterals executed bent over while standing

Now, for a look at the training of the trapezius.
Taking up a triangular space in the middle of the upper back the trapezius muscles play an extremely important role in defining not only the muscles of the back, but the shoulder too, and they’re extremely important for frontal poses as well. The trapezius is most responsive to power exercises, and as such most exercises for it are done with massive weights.

1) Upward rows (standing)
2) Shrugs using a barbell
3) Shrugs using two dumbbells