A good tip that I've heard is that if you drink tea and use tea bags, leave a tea bag to cool off on a plate or something, and when they are cooled, close your eyes and place those on your eyelids. Keep there for 20-30 minutes!
Also cold spoons work, I've heard!
For covering dark circles I use Garnier Roll_on 2-in-1 or something like that. It covers nicely and it contains caffeine so it helps too!