We all have weak areas and the first thing to do is understand what they are. One of the personally satisfying things we can do as a bodybuilder is to pinpoint what our weaknesses are and improve them...at the least making our weaknesses less obvious. And in the best cases, turn them into STRENGTHS! For an intermediate to advanced lifter that has been working hard, for at least a few years straight, I consistently see that weak body parts are often paired a stronger part that is picking up the slack. For guys that have weaker shoulders, they often have stronger traps. If this is the case with you, the first thing you want to do is pay more attention to your training, that you are actually working the shoulders on your shoulder exercises. Keep your traps relaxed and don't pinch them up while working your delts. This will probably require lightening the weight. On latteral raises, look in the mirror. Are you shrugging as you raise the weight? You shouldn't be. Use the latteral delt to lift the weight. I would go light and focus on form. I can get a heck of a pump using the 15 lb DB's. Building the side delt will give the illusion of being wider. Latterals will help this out big time. With light weight go for 15-20 rep sets.
And don't forget rear delts. It isn't often that you see a guy that has too much rear delt. These will imrpove how 3D you look from the side and cap your rear shots.
Try saving your shoulder presses for the end of the workout, when your delts are already exhusted. When you press, focus on squeezing the delts as you raise the weight. How many Lbs you use is secondary to form and how you use the weight.