Originally Posted by big_swede
Do alot of corework to strengthen your mid section, thats were the main issue is likely to be - weak lower back and abs. By core work I mean things like front squats, olympic style squats, deadlifts and cleans all w/o a belt, in addition to situps and back extensions. Also some trapezius /rear delt work like JT show above and highpulls will do you good!
I agree with this. If you make your core stronger, you will have much better posture.