A massive pump and burn did more for my shoulder development than hoisting massive weights. The best pumps occur when you increase time under tension – a contracted muscle restricts blood flow.
Since we can't effectively wrap our shoulders to perform blood flow restriction (occluded) sets, maximizing time under tension is our next best option. This can be accomplished in a number of ways including drop sets, extended sets, supersets, etc.
One of my favorite supersets (which places the delts under tension for over a minute) includes dumbbell lateral raises for 15 reps, immediately followed by an isotension static hold with a barbell for 45 seconds. Perform this superset for 4 rounds and your delts will blow up!