Last week you were a student, and now all of a sudden you have a salary, investment options and a day job. Stay on track by first committing to spend less than you make. Sounds like a no-brainer, but most people can't meet the challenge. Then use the extra money to take advantage of that 401(k). "Most people think of this as running a marathon, not a sprint, so it's okay to pace yourself and do a little bit at a time," says Brian T. Jones, author of Getting Started: The Financial Guide for a Younger Generation. If you contribute just $100 a month until retirement and your employer matches with half, your investment—if it grows at 8 percent annually—could be worth more than half a million dollars in 40 years.