1. Go to a paul chek, nasm or shirley sharman practitioner. They will check out your posture. Ignore anything they say about the one true way [edit - I mean the research is inconclusive - either may work, but all will claim their way is correct].
2. If you already have bad posture you need to correct it. Some good [alternative] ways:
- overhead lifting and overhead shrugs
- heavy front squat holds (just the hold, not the squat)
- go look at at mike robertson or gray cook for corrective exercises
3. If you haven't already tried, go to an ART practitioner. It's very sore but effective for a lot of people.