If you don't have a mentor...find one! ASAP!
A mentor can be a faculty or staff member, teammate, alumni, classmate, roommate, or anyone that offers their time to help you. Mentors are everywhere - you just have to be aware and open to the possibility of having someone assist, encourage, challenge, and inspire you.
Mentors guide you! They can recommend courses to take, people to meet, and things to do (i.e., join the surf club, they have great socials). They challenge you to excel, while supporting and encouraging you along your journey. My mentor in college, who became a lifelong friend, was the staff advisor of one of my organizations. She challenged me to run for Vice President of the organization, which I was elected to, and then encouraged me to improve the organization. I worked a lot harder, but with her support, I succeeded in vastly improving the organization's structure and communication efforts.
Why are mentors so imperative? They take the time to get to know you, discover your strengths, and help you use your strengths to achieve more than you can imagine. If you find a faculty mentor, she may offer advice on courses to take and grad schools to apply to. She may help you find an internship or offer a research assistantship in her office. If your mentor is an older member in one of your organizations, he may connect you with key people, recommend professors, or invite you to attend fun social events that you might not have heard of on your own.
How do you find a mentor? Attend office hours, get involved on campus, meet staff members at campus events. The more people you meet and make connections with, the better chances you have of finding that one person who will change your life.