If just general and not due to injury or disability some exercises I have used are front squats, deadlifts and ESP snatch grip deads, rear felt work like face pulls and bent over db flyes. Pull-ups are also great because of upper back and shoulder stability required. A strong core is important so dont forget abs and back extensor work. I pay attention when sitting, ESP when driving. Just sitting upright and contacting shoulder blades and thoracic extension will help. Also work chest flexibility with stretches. It's a bit of a shot in the dark without specifics from OP.