Hint: Wash your face!

Wash your face before you dive. It helps you look better, so the fish don't swim away in fear. Oh, and it'll help your mask stay clear too. And remember to wash the mask as well before jumping in. A lot of the cloudiness can be reduced if there isn't much dirt on the surface of the mask. And washing your face helps prevent face-goo from getting in.

Also, Coca-cola does wonders on new masks. It helps remove residual layer of chemicals and such that come from the manufacturing process. Plus, Joey says it makes the mask smell good. (Only applicable to Coke lovers).

Both these tips, tried and proven. My explanations might not be scientifically sound, but they sure seem to work!