Which exercises would help improve posture?
I have a mild case of Kyphosis (rounded back).
As always, please make sure to speak with your doctor and confirm that it is safe for you to start an exercise program.
Strengthening the muscles in your posterior chain (your back), especially your upper back, is important to help combat rounding of the back. Pulling and rowing movements are essential in strengthening the latissimus dorsi, rhomboids, trapezius and posterior deltoids to name a few. Those are muscle groups that will support your spine and posture.
Perform a strength training routine that will challenge those muscles twice a week and you may see some improvement in postural positioning. Regularly stretching your pectoralis (chest) and anterior deltoids (front portion of the shoulders) will allow for more range of motion and less tightness in the frontal torso, which will then allow your shoulders to pull back to a neutral positioning.
Try this routine: Pulling/Rowing Workout For Postural Support. Perform this in a circuit or focus on each exercise for a set or two then move on to the next. Either approach will be helpful toward your goal.