When performing any chest exercise focus on bringing your elbows as close together as possible. Forget about your wrists, the dumbbells or cables in your hands. Your pecs do not insert at your wrists. Push your biceps into the sides of your pecs. Don’t think up and down, think elbows in. Besides focusing on your elbows, keep the following in my mind when doing any upper body pushing exercise where you’re supported by a bench: focus on pushing yourself into the bench, do not focus on pushing the weight away from you. This sounds simple and irrelevant when reading for the first time. Try it and be prepared for a big surprise.
Your hamstrings flex the knee and extend the hip. So we have to find exercise groups that make sense for hamstrings. Found them! Leg curls and deadlift variations it is. For leg curls focus on pushing your hips into the pad. The hips should never leave the pad. As soon as your butt comes up you’ve taken tension off the hamstrings and are moving the weight with the help of your glutes. For deadlift variations like Romanian Deadlifts that put the hamstrings in a stretched position, focus on shoving your hips as far back as possible as you lower the weight. Forget how low you can actually go. There is no good or bad position here, just how far back you can move your hips while maintaining a slightly arched spine. As soon as you can’t go any further back you should initiate the concentric portion of the rep.
Due to sufficient stimulus from all chest pressing, front delts are rarely a weak point with any lifter. Therefore I really don’t think it makes sense to focus on a small muscle group that’s already overpowering the other muscle heads (lateral deltoid, rear deltoid).
When performing any lateral variation (dumbbell laterals, cable laterals, upright row), focus on keeping your shoulder blades as stable as possible. There should only be movement at the shoulder joint. Don’t involve your traps by shrugging the weight up. The range of motion for any exercise targeting the lateral deltoid is a lot less than most lifters expect it to be. So make those few inches work in your favor.
For any rear delt exercise like rear dumbbell flies, leaned over cable flies, face pulls etc. think OUT not back (or up). Don’t pull the cables/dumbbells back, only think about pushing them as far away to the side of your body like you’re trying to push away a wall on the left and right of you. This keeps the traps out of the movement. Most people tend to retract their shoulder blades when they do any rear deltoid exercise. We want to avoid that by protracting the shoulder blades and staying in that position as the upper arms travels back.
The elbow joint is a hinge joint. Therefore the triceps can only extend the arm in a straight line. That means if you do any kind of triceps exercise, excessive twisting of your arm or wrists is doing zero good for your triceps so stop doing those bro-twists on the cable station. Eliminate any kind of movement at the shoulder and move the weight exclusively with your triceps. Lock your elbows as well - don’t allow anything to move but your arm as it hinges up and down. Locking the elbows is not harmful if you do it under control. Flex your biceps every rep before you push the weight with your triceps.
I’m pretty sure you have figured out by now that the biceps flexes the elbow. Don’t lie. You’ve done curls before. And you love them. But if you want big arms simply doing them is not enough - you have to do them right. The biceps has the exact opposite function of the triceps, but for the same joint. Therefore a curl is nothing else than a hinge too. So next time you curl it up with your bros, focus on your elbows staying locked in whatever position the exercise you’re doing starts out at. If your elbows move forward excessively you’re flexing the shoulder and take off tension that’s supposed to be on your biceps. Flex your triceps at the bottom of each rep before you pull the weight up with your biceps. I also want you to squeeze whatever bar/handle you’re using with your pinky finger. Think about squeezing everything out of that bar with your pinky. If you’re using dumbbells, supinate the weight. That means you start with your palms facing your body and as you curl up you twist the dumbbell so your palms end up facing the ceiling. Besides flexing the elbow, supinating the wrist is the other function of the biceps.