You can sleep more, some people like me just have that in their genes. I have the worst bags under my eyes, and I sleep around 7 hours a night on weekdays. Also if you eat un-healthy they can get bad, so eat healthier.
I usually just wear concealer under mine and it hides them.
Yes, they can. Usually I get them when I'm tired and very stressed, so maybe try to find something to relax you. Also, Sephora sells a cosmetic that can reduce the puffiness, and then you can use concealer to get rid of the darkness.