For gains in shoulder size, you gotta train for a pump. A massive burn usually does more for shoulder development than hoisting massive weights. Achieving the best shoulder pumps occur when you increase time under tension because a contracted muscle restricts blood flow.
But since we can't effectively wrap our shoulders to perform blood flow restriction (occlusion) training sets, maximizing time under tension is the next best option. You can do this in a number of ways including drop sets, extended sets, supersets, etc.
One of my favorite supersets places the delts under tension for over a minute. Check it out:
Do 15 reps of lateral raises with perfect form, immediately followed by a static hold with a barbell for 45 seconds. Do this superset for 4 rounds and your delts will blow up!