Rounded shoulders can develop over time due to poor postural habits.
Being aware of your posture is the first step. If you think you have rounded shoulders, here are some steps you can take to help combat them.
Regular practice of the following exercises can help lengthen out those pecs that tend to create rounded shoulders if they are overworked and tight. As well as build up stability in the upper back and shoulders to help improve posture for the long term.
Always do the stretches first and then follow up with the static crab position below. The pec stretches can be done one arm at a time or both arms together in a doorway.