Portrait zeichnen lernen?

In principle there are:

https://de.wikihow.com/In-View

You go from the coarse proportional skeleton to the more precise outlines and then to the tonal values. The principle is: Growing towards precision, Detailed, contrast rich.

In this case, the drawing art begins with a very thorough observation of the formal nature of the object.

You need to analyse all aspects of the “form” of the object:

• Proportion of parts, lengths, distances, line profiles, curvatures, bends, angle of inclination …
• then the tonal values: strength of the light-dark contrast, flowing or abrupt transitions, shaping the shades,
• Lines: light or dark, narrow or wide lines, uniform or changing line thickness …

The similarity arises first by millimeter-precise shape fidelity (possibly slightly exaggerated) and secondly by the appropriate reproduction of the colors as gray tone values, i.e. as contrasts of light and dark in black and white.