There are lots of resources available that will put you on the right track toward becoming a marine biologist and any other marine-related career. The guidance and career counselors at your high school or college are a great resource or check out the WHOI marine careers page [2]
Links:
[1] http://csi.whoi.edu/how-can-i-become-marine-biologist
[2] http://www.whoi.edu/page.do?pid=9546
[3] http://csi.whoi.edu/faq/woods-hole-oceanographic-institution-0