You can go to the gym if you can. Hold your neck with a barbell, find a weight that allows you to do eight or four groups in each group, and then do dumbbell front lift (exercise the front of your shoulders), side lift (exercise the middle of your shoulders) and bird bending (exercise the back of your shoulders). The number and times of groups are the same as above.

If you don't want to go to the gym, you can also buy yourself a pair of dumbbells to do the above actions. There is no barbell to make dumbbells and lift shoulders.

Push-ups are also an effective method, but when doing them, put your hands wider than your shoulders.