Traditionally, how do you make a straight face like picrel.
I have problems when allocating the eyes, I even use a ruler and it's always one eye being misplaced.
Or in ocassions, I happen to make the face not symmetrical enough and end up with one side wider than the other.

Supposedly, digitally you have the symmetry tool on certain programs that help you place the face accordingly, but traditionally I haven't found a way out of this, I can only use a ruler and it doesn't work.
How do I fix this in my drawings?