Notice in the first pic with the green check mark: elbows stay directly in front of my shoulder and do not move or lift while curling. They stay pinned to my side/front of the obliques.
In the second picture of mistakes, you might lift heavier weights but they won't do a thing to improve your strength or build muscle.
Top left and bottom left: what I call the chicken wing curl. The elbow flares out and there's little bicep involved. Little bicep involved means little biceps.
Top middle and right: standard and hammer curls pulling the elbows back. This usually results in pulling the weight in and pushing it back out, often caused by swinging and momentum leaving both the concentric and eccentric (lifting and lowering) motions worthless.
Bottom middle: the shoulder shrug. Are you doing curls or shrugs? If you find you have to lift your shoulder and/or arch your back, you have too much weight. Control your motion.
Bottom right: two things happening here. The chicken wing flare out AND lifting too high. When you lift so high that the dumbbells can rest vertically at or above your shoulders, gravity is no longer working against you, you lose all tension and you lose the efficiency. Keep a smooth, controlled motion with time under tension a constant until you reach the fully lowered position. Repeat.
If you find yourself a repeat offender of any of these and can't correct it with your usual weight, drop to a weight that does allow you to do it properly. Then, progress with how much you curl and witness your progress in your arms, both visually and with strength.