Well firstly make sure you're getting enough sleep every night, even if it doesn't seem to help. I take a few sips of water every 10 minutes to make sure I'm always hydrated. Vitamin D and particularly Vitamin K deficiencies are often the cause of dark circles. When you are deficient, tiny blood capillaries can leak around your eyes. Exercise definitely helps, cardio at least does. It really helps with blood flow and it feels like just the bouncing and the fast heart rate or blood flow from running helps drain around my eyes. Sometimes it's just hyperpigmentation, and even if it's not, skin lightening ingredients can help (but they can also be dangerous..). I used to put some azelaic acid I bought in powder form around my eyes... bad idea, but it did lighten them temporarily some days.