My deltoid development has been a result of heavy overhead presses, and many straight arm raises. I use many supersets and trisets.

Sample deltoid workout:

-Smith machine overhead press (smith machine allows you a greater range of motion than with a barbell) (6-10 reps) superset with rear deltoid raises (12-20).

-Dumbbell overhead press (6-10 reps) superset with side laterals (10-15 reps)

-Cable side laterals (in front and behind, 1 arm at a time) 4 sets (left arm forward, right arm forward, left arm back, right arm back, no stopping until all 4 sets are done).