First is to stop flaring your elbows on shoulder press. This causes way too much unnecessary pressure on your shoulder joint seeing as how your shoulder socket is slightly forward. Once you start putting your elbows at an angle forward, you’ll notice that the shoulder pain is relieved and you will start hitting your delts more effectively.
Second is to stop resting at the top of a shoulder press. Often times when people are doing shoulder press, they press the weight all the way back up and lock out their elbows and cheat a half second rest without even realizing it. While you do want to nearly straighten your elbows, you want to focus on the peak contraction of your deltoid rather than locking your elbows out and then as soon as you get that peak contraction, go right back into your next rep.
Third is to stop shrugging while doing lateral raises. Too often, people go too heavy on lateral raises which causes them to start creating momentum and engaging their traps at the top of the exercise. In order to fix this, first you must drop weight.. and then you really want to focus on extending your arms in an outward motion rather than raising up and then also stopping at parallel with your shoulders.
Fourth is to stop resting at the bottom while doing lateral raises. Another issue I see all the time is people brining the weight down too far during delt raises.. in which case, they lose the tension on the muscle and the allow themselves to create momentum at the bottom and start sacrificing time under tension. Instead, start with your arms out at an angle, where you feel the tension on the muscle, and make THAT your starting position rather than bringing the weight all the way down to your side.
Fifth is to stop rolling your shoulders back during rear delt flyes. Rear delts are commonly underdeveloped due to the amount of trap/rhomboid engagement that people get during their rear delt exercises from not doing the exercise right. What you want to do is protract your scapula AKA roll your shoulders forward (and keep them rolled forward the entire time) and focus on pressing the weight outwards rather than back and last but not least, stop just before parallel with your body because THAT is where you should feel the peak contraction.