1. Live within your means.
And I think one thing that people all too often misinterpret about "living within your means" is about saving money. You shouldn't aim to break even with your income & expenses every month. On top of my 401k (which you should definitely have), I also put 25% of my after-tax monthly income directly into my savings account. Living within your means also includes having a "rainy day" backup plan, just in case. Not to mention saving up for your future expenses... AKA - buying a house without a huge mortgage.
2. Be a sponge.
3. Take care of yourself.
- You won't need to live off of 4 hours of sleep a night, unless you choose to do so. Of course, there are going to be some times when you'll need to stay late or bring a project home, but for the most part, you'll be able to develop a regular schedule for sleep (dare I say, a bedtime??). Along with that, you'll wake up at the same time everyday, which will finally allow your body to form regular sleeping habits. And I've noticed that has helped keep me from catching small colds every now and then.
- You know exactly what days & times you will have available to set a workout schedule. I spend one evening each week playing in a soccer league and I take morning jogs with a friend every couple of days. In school, I never knew what nights I would be slammed studying for huge tests or what mornings I would have the energy to get up even one minute before I absolutely had to.
- The fridge is solely your domain. This is my first time living without roommates, so I'm the only one to decide what snacks to bring into my home. If you keep only healthy, fresh foods at your house, you won't be tempted by the junk you used to eat regularly in school. You can (and should) really take advantage of that to keep your diet on track!