Start with a sheet of paper, and draw it in perspective.
Start bending the sheet, like it is a part of a cylinder. Add a center line. Draw many in different orientations. Try it, it’s fun!
You can also first draw a rectangle in perspective, and construct a curved sheet on top of that.
Try to draw lines that follow the bend of the sheet of paper, and tangent lines at the center line. These will help you place the facial features.
Intermezzo: you can draw ellipses by constructing them from perspective-correct squares.
Draw a box in perspective, and apply this to two opposing sides.
Add facial features.
Try to construct the rest of the head also.