When I got my essay back I was surprised by the amount of mistakes I had made since I had the feeling of having done a good job on the paper. All of my mistakes were either gramatical or structural, these kind of errors happen all the time but are possible to avoid by proofreading and analyzing everything that is said.
I learned that it is not only important to focus on what is said, but to also pay attention on how it is said. The most important thing I can do to improve is to stop summarizing and start analyzing.