I have taught a few people since I received my instructor rating. The most common mistakes I have seen are.

Rolling the wrong way. A lot of students have admitted to me that sometime they don't know which way to roll so they will guess and if they are wrong they will just roll the other direction.

Landing too fast or slow. Usually they are too fast, I think this is a safety thing.

Landing a long way away. About 90% of my students landings are on the far side of the runway.

Flying over their head. The easiest way to become disoriented.