No matter what your shoulder width, deltoids cannot be over developed.
Advanced lateral raise instruction from the Steve Davis "New Breed" bodybuilding courses.
The most common mistake body builders make is over development of the frontal (anterior) head (due largely to an abundance of pressing movements) at the exclusion of the lateral (side) and posterior head.
Before the deltoids will ever look impressive, all heads must be developed equally!
Also, never train your trapezius muscles separately. They get enough work from delt exercise, no matter how "pure" you try to make it.
Overly developed traps can ruin any attempt at increasing your shoulder width, so be careful.
Two-way DB lateral raise
a. Do 6 sets of 12 repetitions.
b. Rest 10-15 seconds.
c. Use a "false grip."
d. Stand erect, knees slightly bent.
e. Start with your palms resting against the outside of your thigh. Slowly, with slightly bent arms, raise the dumbbells while rotating your thumbs down, in an arch to a point 2" past the ears. Perform 6 reps, then;
f. Bend over at the waist and perform 6 reps bent over lateral raise, again rotating the thumbs downward and raising the dumbbells to a point just past the ears.