I was a barber, not cosmetologist, of course there are textbooks but more focus on chemistry and techniques than what style fits who - we just cut anybody's hair the way they want.

Are you looking for yourself or as a career thing? I don't know if there is a fashion advice community here. In general terms you need to consider whether you want to highlight difference or mute it. So a big round curly cut on a round face will emphasize the roundness, a cut that discourages volume, flows vertically, like a shag, will offset the roundness. On a heart shaped face, often people like to emphasize that with straight cut bangs (fringe), you would mute the shape with a style with volume at chin level.

If it's a career thing just look at lots of pictures of haircuts, you will learn, but give people what they want not what you think they should have. It's just hair, it grows back.