It is good to see somebody so motivated to start GMAT Preparation from 2nd year of college. Assuming you are new in this forum i will suggest you to start from General GMAT Questions and Strategies- New to GMAT START HERE forum . This will guide you through the nuances of GMAT. Since you are only in 2nd year i can safely assume that you are not taking GMAT within the next 3 years (Unless you are going for Young Learner's Program in ISB or other reputed B-Schools). GMAT score is valid for 5 years after test date. But mostly people take GMAT a year or half before applying to their dream schools. But you must know that GMAT is not an end in itself, just a means to an end. No doubt a good GMAT score will give you an edge but its not everything. Your profile bears the most importance in B-School admissions. I would suggest you to choose your dream B-Schools and find out the profiles of the admitted students(Available here). Being in 2nd year in college will give you ample time to strengthen your resume. So you should commit more time to that.
For getting good GMAT score i would suggest you to go through this share GMAT experience forum. This will give you a fair idea about the means to secure excellent scores in GMAT. All the books and methods of preparation are discussed here. I hope this post will help you.