Apart from practicing deep breathing periodically, you might want try getting a lacrosse ball and using it for deep point massage. I was able to release a lot of tension from my neck and shoulders with one. Also, a theraband was recommended to me by a physio so I could do flys to help pull my shoulders back into proper alignment.

I'd recommend seeing a physio - one did me the world of good and was able to suggest exercises and make me aware of what good posture looked like. I've had to do a lot of core strength work to fix bad habits and now I feel much better.