Start with the shape of the face. Draw an oval if you do not have an exact reference. If you have a reference, such as a model or a photograph, copy the shape from the reference.
Find the exact center of the shape you've drawn by using your ruler. Measure from the top to bottom and draw a line down the center of the face. Keep the ruler there and mark the middle of the length. (If your face is ten inches long, you would make a mark five inches in). Then draw a line from side to side through this mark. The result should be a cross inside an oval, with the cross at the exact center of the oval. Split the horizontal line into fifths using the ruler. (For example, if the line is five inches across, make a mark every inch). Sketch small ovals for the eyes in the second and fourth fifths. Later you can go back and sketch in the details.
Measure the length of one of the fifths you created in Step 2. Move down the vertical line from the horizontal line by a fifth and make a small mark. This will be the tip of the nose. Measure down from the mark by another fifth and make another mark. This will be the middle of the lips. Move down one more fifth and you should be at the base of your oval (the shape of the face).
Sketch in the shape for the lips. If the face is smiling, the smile will be the same length as the distance between the pupils. Sketch the lips, keeping the mark you made in Step 3 as the place where the lips part.
Sketch the nose from the mark you made in Step 3 to designate the tip of the nose. The base of the nose will be about the same length as one eye shape. Sketch the nose, making sure both nostrils are the same size.
Begin the hairline, which on most people begins about one fourth of the way down from the top of the face. This will change depending on the person and whether or not their hairline is receding. You can shade in the actual hair later.
Draw the tops of the ears at the same height as the tops of the eyebrows. The bottoms of the ears will be the same height as the top of the lip. When you are done, shade everything to add detail. Place the eyebrows just above the eyes. (There is no mathematical formula for placing them.) Depending on the person's expression, the eyebrows may be higher or lower.