Attend all your classes every day even if you have a job and other responsibilities. There is an inspiring story of a working mom who balances med school with the rest of her life at Mom MD (see Resources below).
Pay attention in class, take notes, participate in the discussion, and ask questions.
Study as much as you can to enrich your classroom instruction. This includes reading textbooks, researching additional information, and supplementing assignments with real-world clinical or hospital work.
Read as much as possible about what you are studying even if it is outside of the syllabus. You will do well by enriching yourself with additional knowledge.
Schedule time with your professors and advisors to ask questions and seek their advice on how to do well during the semester with them. The Princeton Review offers study suggestions like these on their website (see Resources below).
Supplement your class time with extracurricular activities or volunteer work at a local clinic or hospital. Seeing what goes on in the real world will help you better apply what you are learning.