It is common knowledge amongst lifters that the back needs to be set tightly for the deadlift. But more important is that both the front and back of the torso are tight. When tightened together they will balance out tension in the upper body and protect the low back from overarching, which can lead to problems. This is especially important for those with excessive curvature in their low back. The front and back of the body work together for full torso tension and protection of the spine.
Too frequent use of alternating grip
In order to develop a strong grip the hands need to be stressed appropriately. Use double overhand grip whenever possible. When this grip starts to reach its limits then start to condition yourself to using a hook grip. This will probably hurt a lot at first. It is best to start using the hook grip in some of your warm-ups to begin the adaptation process. Some find that the pain goes away with some diligent practice. Others don’t seem to get through the discomfort. When is the time to use the alternating grip? Maybe never. Unless you are competing as a powerlifter it is questionable if the positives of using this grip to allow for a heavier deadlift outweigh the negatives of using the grip. The alternating grip, when used to lift very heavy, can cause great stress to the bicep tendon and to the shoulder. For some this is worth the risk. Even so, it is best to use it only when necessary.
Not enough attention to keeping the bar on the legs
During the deadlift the lats have a job to do: to keep the bar on the legs. During lighter sets one can get away with having the bar come off the legs. It will not work so well when the bar is heavy. We need to remember that lighter weights are practice for heavy weights. If we do not lift the weight the same way when we practice then we cannot expect to lift it well when things get heavy. Do all your reps with the same intent.
Not finishing the pull
Lifters with very tight hip flexors may not even realize that they are not completely locking out the bar at the top of the lift. Focus on abs and glutes tightening together at the top. Both of these muscles groups will help protect the low back and help prevent over-extension. It may be necessary to do a lot of supplementary hip flexor stretching and glute strengthening.
Too much use of touch and go
There are many important elements to good lifting. These include setting proper tension and good breath control. Touch and go reps do not allow proper attention to either. Ensure that the bar stops on the floor each and every repetition and that proper tension and breathe are being reset every time.