First let's take a moment to look at proportion. Because we're drawing cartoons, we don't have to worry about it too much, but using some standard proportions will help your drawings look good. The first thing we need to know is that faces are basically built on crossed lines to keep things fairly balanced. On the left is a typically proportioned face as in real life. On the right is a cartoon face. See how they're similar?
Notice that the eyes are about half way down the face, the nose is another quarter of the way down, and the mouth is also another quarter of the way down from the nose. Simple, huh? Why not try drawing an oval and marking these lines in, to help you remember.