TRSE: How To Draw Tutorials:
Drawing Front View of a 'Chibi' Character.
Step 3

    To help keep the characters standing straight up without leaning, just draw the vertical line really straight up with a ruler and that vertical line also can help keep your drawing look symmetrical (two alike sides). The vertical line must go thru the center of the head (don't worry about the rest of the body).
    Now draw a horizontal line where the eyes will be sitting on, and this line will help level the entire face including the eyes. It's possible to be able to draw that horizontal line without ruler but it's something it'll take time to master, and I tend to trust my good ol' drafting ruler lot more than my own hands, heheh. ^_^;;