[codingdave]

There are a variety of methods. Some people will teach you formulaic approaches to drawing people/faces, and instruct you to always lay out the 'proper' measurements that most people fit, then just add detail. More traditional methods teach you to draw what you see, but focusing on the structural lines and forms of the person, while merging it with knowledge of anatomy, perspective, and lighting. And other methods are purely 'draw what you see', without additional context, trusting accurate copying to paper to look correct.

What any specific artist uses will vary greatly. But it usually falls into one of those three camps.