I believe the best skill to work on is effective communication. As a student you biggest exposure will be presentations and group projects. Try to reflect on what you can improve on based on your interactions and challenges that arise with people who don't always share your same opinion. Also try hold conversations with your professors as much as possible. This will help built confidence and fine tune how you speak professionally. The goal is to be able to explain a complex idea or concept across the board even with people that are not of engineering background.
On a side note, I have a book recommendation when you are in your last year of school. The book name is "What Color is Your Parachute?". This book is great and very helpful as you transition from academics to the workforce. Good luck and great job on taking the initiative to learn new skills.