Pull-up

You kip or swing the legs to generate momentum instead of pulling from a dead hang.

You cut the top short, getting the chin to bar level by craning the neck rather than actually clearing it.

You drop out of the top instead of lowering under control, wasting the half of the rep that builds the most strength.

You start pulling with bent arms, never returning to a full hang between reps.

Set the shoulders down away from your ears before each pull; the first inch of movement should come from the shoulder blades.

Think about pulling the bar down to you rather than pulling yourself up, and lead with the chest.

Take the lowering phase slow; if you cannot do full reps yet, slow negatives are how you earn them.