If you goal is to prevent shoulder injury than you must take into consideration these modifications. This is what I call the five reasons I can't bench press 450lbs

The first reason is the Dumbbell Fly are stretching the shoulder way too far.
By keeping the elbows straight and over stretching at the bottom of the movement you are putting you shoulder in an un-natural position and possibly causing shoulder injury. The correct way to do this movement is to bend at the elbow, like your hugging a fat girl (what? Fat Girls need loving too) and remember to bring arms down only to the point where the elbow is level with the center of your rib cage.

Bad form doing Dumbbell Bench press
This exercise is sometimes used in place of straight bar bench press for many people with shoulder injuries. The funny thing is that most of the time it's done incorrectly and does not help in shoulder recuperation at all. Most of the time this is done with the arms much too close to the body and the weight coming down much to far The correct way to do this exercise is to lower the weight only until the elbows are level with the shoulders and slightly away from the body. The push up and inward at the top of the movement.

The behind the Neck Shoulder Press
Doing behind the neck should presses feels un-natural doesn't it? That because in order to get enough range of motion to grow you have to put your shoulder in a compromising position for injury Drop this exercise all together, and replace it with front shoulder presses. When doing shoulder presses to the front push all the way up just before lock out and come down only until the elbows are parallel with the floor. For most people that puts the bar just at eye level at the bottom of the movement.

The Lat Pulldown to the back of the neck br This is one that I only see women do for some reason. Once again it doesn't even feel natural, does it? The correct way to do this is to arch your back ever so slightly, and with a shoulder width or less grip pull the bar down until it touches the middle of your chest. I see guys in the gym come only down to about eye level, and other guys all the way down to the chest. I really believe that either way is correct as long as the movement seems natural. Once again you can prevent shoulder injuries by not doing this exercise to the back of the neck.

I think while we are on the subject of pulldowns we should include The Pullups. I get more resistance form people that I train when I tell them the way they are doing pullup may be the cause of their shoulder injury.
This particular exercise has two different incorrect variations. The first is to pull to the back of the neck. I think I stressed the problem with any exercise going to the back of the neck already.

The second incorrect variation to the pull up is to select too wide a grip. For some reason many people believe that the wider the grip the wider the back muscles. I don't have time to go into the function of the muscles, but understand, if you want to build a big wide back you are more likely to do so with narrow and medium grip pull up then you will with wide.

The correct way to do pullups is to grip the bar at shoulder width and pull you body up until the chest meet the bar, or use a "V-Bar" or chinning triangle over the pull-up bar and pull upward until your chest touches the chinning triangle.

By making these simple modification of common bodybuilding movements you will be preventing shoulder injuries that can sideline the results that you work had for and ensure.