Fogging and leaking are something which all scuba divers will have to deal with. The only thing more annoying than your lens fogging up or water dripping down your face to pool at the bottom of your mask, is both happening at once. Thankfully there are some things which you can do to prevent them.
If you do have water getting into your mask, then you may want to try loosening your straps. It may seem counterintuitive, but if your mask is too tight, then the skirt can splay, and the seal can be broken. The underwater pressure should keep your mask on your face. As long as you are looking down, the mask will be sealed. If you look up, the air in your mask may force the mask up and off of your face.
Some masks come with anti-fog technology. You can also buy an anti-fog spray to use on your mask when you are diving. If you do not have any anti-fog spray, then there are a couple of household items which you can use. Rubbing dish soap or toothpaste on the inside of your mask can stop it from fogging up in the water.
Related Post: Scuba Mask Leak