The most popular place to use the highlighter is the cheekbones. You can apply highlighter on your cheekbones to highlight your bone structure and make your face look thinner.
If you want to narrow your nose, apply highlighter vertically to the bridge of the nose.
If you want to create a full lip look, then you should apply some highlighter to the curved area in the middle of your upper lip. By highlighting this area, your lips will appear prominent and larger than they are.