All professional schools have specific requirements for entry.
Whether you plan on medicine or optometry, dental school or chiropractic, your first job is to find out what your chosen professional schools will require of you. In many cases there is a specific national qualifying exam, for example the MCATs for medical school. These are often exhaustive and will require you to invest a lot of time preparing for them. Do not expect that a short-term cramming period will work, study steadily for a year or more. There are books to help you with all of these exams as well as courses, such as the Kaplan series.