Take time to figure out why you want to volunteer. Do you want to network and meet new people? Need extra classes for school? Want to travel or take time off from school? If you decide what your goals are, even if you don't know all the answers, you can let the answers unfold as you go through the process.
Volunteering is a wonderful way to see if you want to pursue an interest and develop it into a career or hobby. Its a great way to test out a possible profession to see if you really like it, or get more experience in a certain field or skill. Many people use volunteering as a way to make a career transition, prepare for a career or if they are retired -- to stay active and share their knowledge.
If, for instance, you want to pursue marine biology but aren't certain whether you want to primarily work in a laboratory or do mainly field work, find an opportunity to work in a lab on a mariculture research project or help on a horseshoe crab project sponsored by Earthwatch. If you want to learn more about Wild Horses and Burros, contact the Bureau of Land Management (BLM). All the major green volunteering sites, with local and global options, are inlcuded at http://www.greenyour.com