Most of the guys benching in the gym are bench pressing wrong. That is surefire way of fucking up your shoulders. I strongly recommending watching some videos from Scott Mendelson about improving your technique. I've linked one of them here.
- Retract your scapula - Imagine a ball plached behind your shoulder blades and try squeezing it in.
- Arch your back(not excessively like those powerlifting fail images).
- Bench is a sitting down squat. You have to plant your feet firmly down the ground and push through the inside of your thighs to power the bar back up. Not using legs is retarded.
- Do NOT bounce the bar off your chest. Let is gently touch your chest and then push up.
- Bar having to touch the nipples is wrong. It should touch anywhere from nipples to top of your top rib cage. Where it touches will depend on a bunch of factors including body symmetry.
- Use ring finger around knurling to know the bar width to hold.
- Breathing is extremely important - goes without saying.