Dark circles occur due to various reasons. Treatment depends on the cause and type of skin you have. Avoid long hours of reading or computer work. Give rest to your eyes and take enough sleep. Avoid rubbing eyes. Treatment under supervision of a qualified dermatologist in form of certain creams and chemical peeling sessions will improve its appearance. Maintenance will be needed after achieving desired results. Don't expect magical results and cure for it as it's not a disease. Hope this helps.