is it better for a pitcher to narrow bench or regular bench? i have to do one for weight training
Neither is that beneficial - particularly for pitchers. Instead, try one arm dumbbell bench presses, different push-up variations, and dips.
find what feels best on your shoulder. I use a slightly wider than shoulder width grip, elbows around 45 degrees to body, not flared out, and i make sure to keep my upper back tight through the entire lift. Think about pressing off of your traps, not your mid back. This will ensure you get a good arch and are keeping the back tight throughout the lift.
Just to add what Lanky said - make sure you setup properly and don’t forget that the lower body does contribute on the bench press - so pull the feet in more under the body and tighten those butt cheeks during the lift!
Not many benchers understand that it is a full body exercise. I recommend using a neutral grip when benching, If your gym has a swiss bar I’d recommend using that.
This is a swiss bar http://flexcart.com/members/elitefts/swiss-multi-bar-400.jpg