The "bus driver" exercise is where you hold a plate at arm's length in front of you and rotate slowly. It's a hugely underrated shoulder movement.
This exercise puts the whole deltoid group under constant tension and works angles that aren't normally trained in the gym. It's an excellent way to finish a shoulder workout and make the joint more resilient to injuries.
Add the 3-Position Front Raise
Pair the bus driver with the front raise using three different grips: narrow, shoulder-width, and wide. (See video.)
Using the different grips makes this a mechanical drop set: When you can't do an exercise any more, you continue to do reps by changing the leverage. By taking a wider grip you shorten the resistance arm, which will make the movement a bit easier, allowing you to get more reps in without having to decrease weight.
The change in grip might also bring some new motor units into the mix, which is a benefit since the more motor units you recruit and fatigue, the more you'll grow.
A. Bus Driver 6-8 reps per side
B. Front Raise dumbbells about 1-inch inside shoulder-width, 6 reps
C. Front Raise index finger in line with outside edge of deltoid, 6 reps
D. Front Raise wide grip, 3-4 inches wider than shoulder width, 6 reps
We're shooting for 6-8 reps per side for the bus driver exercises and about 6 reps for each of the three grips on the front raise, but really the goal is to fatigue and to pump up the muscles as much as possible. If that goal is accomplished, it doesn't matter if you did 5 or 10 reps per position.