Please, refer to other post for more detail. I already have posted about some of these and I plan on posting about the rest in the future.
#1 I would have worked less and concentrated on my classes/grades more. Having a job was very important for my self – discovery and my resume, but I could have worked less hours.
#2 I would have got a better GPA. I found out the GPA was very important if you wanted to make yourself marketable to your ideal company. Even if you just want to move on to graduate school, GPA is important.
#3 I would have got to know my classmates. I wish I would have got to know more people in my classes. They are a factor to good grades and a better career.
#4 I would a joined a club and/or student organization much earlier. I would have met my classmates in these groups. The networking experience and company information I got in one year was extremely valuable.
#5 I would have got to know my teachers better. They can be a great resource for your career. If they see you more, they know your trying. Lastly, you may end up needing a letter of recommendation from them.