Summarize this article in one sentence.
Try to make small, measurable gains with each workout. When you work out your shoulders, lift heavy, and stick to 4-7 reps per set. Increase either the weight or the rep number very slightly with each workout. This way, you'll set a pattern of incremental, sustainable gain.  Keep a practice of "progressive overload." Lift more and more weight over time so that you are always pushing the limits of your muscles. You will not get bigger shoulder muscles without getting stronger. Imagine that in your most recent workout, you lifted a 55 lb. dumbbell shoulder press in sets of seven reps. Next time, push yourself to do eight reps with the same weight. Alternately, move up to 60 lbs and do seven reps again. The deltoid (shoulder) muscle comprises three sections: the anterior (front) head, the lateral (middle/medial) head, and the posterior (rear) head. Try to build muscle in each of these areas in order to balance out your shoulders. The wider and thicker your shoulders are, the more impressive they will appear.

Summary:
Lift heavy weights, and focus on steady gains. Develop all three heads of the deltoid muscle.