Your delts are a lot like your calves, they're involved in A LOT of the movements you do. And like your calves they need heavy weight at high volume, ie: lots of reps, lots of sets. Range of motion is a big part of it as well since they have such a large rotational coverage area. When you press, press heavy but shoot for a minimum of 12 reps, unless you're going purely for strength. And bring the bar as low as possible. When doing raises, lateral or otherwise, no quarter or half reps. You want your hands to come up at least even to your shoulders, and if you can come up to eye level, even better. When your shoulders start burning, that's a good sign, but keep going through the burn. And lastly, make sure you contract as fast as you can, and release slowly. Fiber recruitment and time under tension is often neglected during shoulder training. Hope this helps.