Attend all timetabled lectures, classes and practicals; make this your top priority and fit everything else around that.
Prepare a personal timetable and schedule of times for preparation and revision.
Use whatever means necessary to remove distractions and temptations; consider working in the College library rather than your room to make yourself 'unavailable'.
Be careful about which textbooks you buy; try them out first using College or Departmental libraries until you find ones that suit you best.
Keep fit and healthy - schedule time for relaxation and exercise.
Networking - academically and socially - is important. Get yourself noticed and involved in College and Departmental activities; always reply to formal invitations - before and after events.