Involvement in various organizations helps to shape your overall college experience and I highly recommend it! Greek life is typically at the top of most college students to do list as it is a great way to meet new friends, forge large and strong networks, and (lets face it) engage in some great social activities. However, this is not the only route one can take. I would encourage you to identify what type of career interests you have and join an organization that will add value to the academic portion of your college career. Sometimes these types of organizations will lend you more practical experience that can be applied to your future career as well as building your network.
As you venture into different activities and educational or social clubs, make sure you prioritize your school work first. If you complete your homework and studying first, you'll have time to set aside to engage in the clubs and organizations. College offers many variations of class schedules which allows you the opportunity to create as much free-time as you see fit. For example, after my sophomore year I found that having classes on Tuesdays and Thursdays worked best for me and my social interests. While I was in class all day on these two days, it freed up more weekdays and weekend time for me to complete assignments, hang with friends, volunteer on different projects, etc.
If you find that your grades are falling, you're having a hard time staying awake in class, or you miss several classes, it is probably a good idea to trim some extracurricular activities until you can refocus on the reason why you're in college in the first place. Once you have reexamined and realigned your priority, you can begin to add extracurricular activities back into your schedule one at a time.
Good luck on your college endeavors!