Work your shoulders. Try doing movements such as the military press, the Arnold press, lateral and anterior shoulder raises, push-ups and, of course, rotator cuff exercises. The best technique for these exercises can be found on the internet and in books.

If you are capable to do that, perform push-ups and military presses with dumbbells. The proper technique is to hold the dumbbells beside your ears, with your upper arm parallel to the floor and your forearm pointing to the ceiling, with arms bent at roughly 90 degrees. Push the dumbbells up and together and then lower them back to the starting point. That is 1 repetition; repeat 8 - 12 times with the appropriate weight.

Stand tall and wide. Try to fix your shoulders high and back and suck in the gut. Posture can make a big difference in the way you look. Proper stretching can also make your shoulders look wider. Try this. Put one hand on the wall and make it face one way and start turning your body the other way till your shoulder gets tense and then repeat.

Swim. Swimming will burn off fat and works nearly every muscle in your body, and almost everyone can do it. Over time, a vigorous swimming regimen will significantly widen your shoulders.

Some tips for your help

Wider shoulders make your waist look slimmer, and in turn, a slimmer waist makes your shoulders look wider.

Because it makes your waist look slimmer, your shoulders will look wider if you tuck in your shirt.