If you are doing a professional picture and need accuracy, this has helped me tremendously. This is MY TIP of the day and it is LONG! Skip it if you want to.
Those crazy lines help with placement too. Don't get me wrong, I mess up majorly most times. What? I can hear you say, "Your pictures are near perfect!" Not when I'm working on them. If you feel something strange in your gut about your picture, put it up to the mirror. That'll tell you. And take your reference pic and put it in the mirror... what a whopper difference!
Take an envelope, piece of paper, ruler (straight edge)... anything to vertically represent your line placement. For one example: Take your reference pic, put the straight edge against the edge of the smile line and see where it lands near the eye. Then do the same on your drawing, if it doesn't land in the same place, adjust. Friends & artists, I'm not ashamed to say I had to erase this woman's mouth twice. So don't give up. Take a deep breath and work slowly. It's like molding clay.