You should only focus on certain body parts if they are "deficient" compared to the rest of your body (focus on your back if your pecs are disproportionately strong). If that's not the case you should look to work every major body part (shoulders, back, chest, triceps, biceps, quadriceps, hamstrings and traps), otherwise you'll cause an imbalance that will eventually lead to a chronic injury.

In your case, having a history of back support problems it's a good idea to focus on that for a while.