I'd personally say to use guide lines. I useful tip is eyes are eye length apart, and the nose should fall in the area between the eyes. If your struggling with facial expressions, try making agusting the size of the eyes. You can make one eye smaller or larger, or you could make the eyes wide open. Eyes are a decent way to express emotion. Looking at refences is also good. I am still struggling with mouths, so I don't have any tips on those.
