Dark eye circles can be a hereditary thing too. But a few things that should help:
1. There are several undereye circle roller ball serums. I specifically use Garnier, but CVS makes a similar version for about 3 bucks less. (As a PP said, It is NOT makeup or concealer)
2. Using cool green tea bags on your eyes for about 15 minutes. Then wash with an anti aging face wash.
3. Cucumber slices on your eyes. It reduces the dark circles by decreasing the blood flow to the area much like a bruise.
4. A good nights sleep. If you have a problem falling asleep I have found that taking 5mg of Melatonin helps tremendously.
Other reasons why you might have them are, Smoking, Allergies & Stress.