With hundreds of different exercises, and thousands of variations, people commonly do a few of these incorrectly. But fear not, we're here to help give you a quick form check, so you don't make the mistake of doing one of these wrong (and potentially risking an injury).
The granddaddy of all strength training exercises. The problem that many people have with the bench press is a limited range of motion simply because they are trying to lift too much weight. This includes going all the way down for a quick pause, and going all the way up to complete a rep. Go with a full range of motion and keep the speed consistent. After a while, you can work your way up in weight while maintaining that same form.
A great compound strength movement that trains many muscles at once. However, just like with the bench press, people often only go down maybe half as far as they should for the full benefits. And unlike on the bench, where you know you've gone all the way down when you hit your chest, you don't get that same feedback while squatting. To double check your form, set up a box slightly below parallel, and hit some reps when your ass touches the box. Then when you take away that box, try to maintain the same ROM. Go with a lighter weight, keep your form tight, and get down low. You can also set up a video camera to double check your form between sets.
If your whole body is sagging as you perform pushups, there is a problem. Your posture should be like a board as you go up and down. From the back of your feet to your shoulder blades should ideally be one straight line. So if notice your hips are touching the floor before your nose, something is wrong. Work on tightening your core to keep your posture straight.
Numerous people lean way too far back as they try to push the bar up above their heads. If your form is making chiropractors around the nation all grimace at the same time, go with lighter weight and work on your form. Pretend like you're pushing your head through an imaginary window once the barbell clears your forehead.
Dips are great at building the chest and triceps. But this is one of those exercises where going down as far as you can is not recommended. Your arms should make a 90-degree angle when you are at your lowest on a dip. You could end up hurting yourself if you are going down any farther.
Using a little body movement while doing dumbbell bicep curls is fine as you try to squeeze out every rep. Even most of the pro bodybuilders swing a bit as they lift those heavy dumbbells. But if your body is behaving like a tree blowing around in a tornado, you are asking for an injury (and your biceps won't grow as much). If you want to get more out of a rep, focus on flexing as hard as you can while you move the weight (this is called the mind-muscle connection). If you do it correctly, even 15's will feel hard after a few reps.
Once you get the weight up, focus on how far down you're going at the bottom of your rep. You should stop once your arms reach a 90-degree angle, and going down any deeper than this is not advised.
Another exercise that keeps chiropractors busy. Bent-over barbell rows are a perfect compound exercise as it hits biceps, back, and lats. But if you are arching your back while doing them, it is just a matter of time before your spine starts to feel it. A good way to double check this is by filming your set from the side. This will allow you to quickly see if you were rounding your back to get the weight up or not.
So next time you are at the gym, keep these thoughts in the back of your head as you're running through these exercises. This works for any exercise really. Take one of your sets and just use it to focus on form, don't care about how many reps you get.
If you want to share your new knowledge with others, make sure you go about it in a non-arrogant way. You may mean to be helpful, but angry people with weights in their hands can be detrimental to your health.