Plan your class schedule, as much as possible, so that your classes are consecutive. This avoids potentially inefficient downtime in between classes.
Get a daily planner and plot out each day's classes and errands the night before. Schedule your errands to avoid backtracking.
Use downtime to do schoolwork. Finish that chapter on Aristotle while you're waiting outside your professor's office.
Keep a textbook or other schoolwork with you throughout the day. You never know when you might have time to kill in line at the post office or in the doctor's waiting room.
Avoid distractions that get in the way of your schoolwork - use fun activities as rewards when you've finished your day's work.
Make sure you schedule in a healthy amount of fun time. Efficiency is useless if it drives you insane!