Push or Pull?
When it comes to upper body strength it’s important to balance the pushing and pulling muscle groups.
Most people are biased towards an upper cross syndrome posture which is a displacement of your head and shoulders forward. This will place undue strain on the posterior neck and shoulders.
In spite of the poor postural alignment you should focus more time stretching the front or chest and biceps and strengthening the back and develop pulling strength.
With consistent effort you will start to correct your slumping posture to more upright and feel much stronger!