Advice needed to help with shoulder posture

[RJB_666]

When i first started weight training i wasn't shown everything and basically didn't train balanced. It even got to the extent of not training back for a while due to an injury. This has caused my shoulders to come forward rather than lie in correct posture. I still have the problem even though i am now training balanced. I have even tried training rear deltoids a bit more but i am not noticing much difference in posture. I'm hoping that some of you guys know of a better way to train to strengthen needed parts to cure this.