my chest was really stagnant until I changed my form. I keep my elbows close to my body and use more of a powerlifter form and I think that has helped tons. I also do about 7 different exercises for chest all benches and flys I can think of. I go as heavy as I can and concentrate on getting the pump and feeling the muscle do all the work. Just started this routine in like april but I can already tell a difference.
I was always shoulder dominant on the flat bench as well and was constantly having shoulder pain until a power lifter helped me out with my form.
He pointed out that your elbows should be down by your side, not splayed out wide (which puts all the stress on your delts and will eventually rip one). Think of it as if your were trying to push your buddy's car out of a ditch, you wouldn't lift your elbows out to the side, you keep them tight to your body for maximum power.
At the bottom of the lift the bar should hit you in the shelf beneath your pecs and above your abs. The motion isn't straight up, but an arc so that at the top of the lift the bar is above your shoulders. You also want a slight arch in your back.
Changing to that form has made me sore after doing the flat bench for the first time and the pain in my shoulders is gone. I can also see a noticeable improvment in my chest development.
On chest days I follow up flat bench with incline dumbell bench, weighted bar dips, and across the bench skull crushers.
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