A COMMON MISTAKE I SEE PEOPLE MAKE IN THE GYM #1.
Dropping the weight too fast on the negative part of the rep.
The question that everyone asks is "How much can you lift?" Therefore it's natural everyone to be concerned only with the positive (concentric) part of the rep.
However, what you should be concentrating more on, is the negative (eccentric) part of the rep.
If you were to perform only positive reps or only slow controlled negative reps with the same weight, your DOMS would be twice as big from the negative reps as they'd be from the positive. That tells you something.
Take home message: slow down on the negative reps to get more results from your training.