#1 Be On Time
Professors don't like when you're late to class, and employers like it even less. Learning how to be on time now will save you from being an unemployed outcast later in life.
#2 Show Up
Showing up is even more important than being on time. If you're supposed to be somewhere, be there. It's good practice. Someday you'll have a job, where showing up everyday is a requirement.
#3 Try Hard
You should never settle for less than your best in everything you do. When you actively strive for success you are much more likely to achieve it. So in short, leave your minimalist attitude in high school where it belongs.
#4 Be Organized
Disorganization can lead to serious time management problems in school and on the job. You can save yourself a lot of headaches if you just get it together now. Things to organize include: your schedule, your desk, your closet, and your bedroom.
#5 Write Stuff Down
Humans weren't meant to remember everything--that's what computers and notepads are for. If you get in the habit of writing down the important stuff now, you can develop a habit that will save you from forgetting important stuff (like project due dates and the boss' birthday) later on.
#6 Think Before Speaking
Not everyone embraces this philosophy, but it is a prudent habit to pick up. When you speak without thinking you run the risk of sounding rude, ditsy, or immature--three traits that employers (and a lot of other people) despise.
#7 Learn to Manage Stress
Stress is just a part of life. The sooner you learn to deal with it, the better off you will be in life and your career. Since everyone handles stress differently, you may need to try a few things until you find the stress management techniques that work for you.