Dont neglect your stabalizer muscles and ligaments. Try putting your weight on the bar, lowering at a quick but controlled manner, and lifting explosively to the top (with a spotter) do as man reps as you can in 30 seconds, repeat 3 times.
Alternatly, try dumbbell presses, keep your elbows close to your body and keep a tight controlled motion, it will work your core nicely. Body weight exercises are largely neglected and are really good at practical strength. Finish with incline and military pushups.