How to Clear a Scuba Mask?
After breathing, there is perhaps no skill more fundamental than mask clearing. While other skills, such as gear assembly, are a requisite part of getting in the water, they technically could be done by someone else (although this is not recommended). Mask clearing, however, is a solo skill, and the inabiility to perform it will easily ruin a dive.
Once mastered, this is a skill you will use immensely. I frequently perform mask clearing not just when water leaks in, but also when I insufficiently apply defog. Mask fog can ruin an otherwise good dive, but with, ahem, fluid mask clearing skills, one can quickly and easily remove fog as it appears and continue with the dive.