As the name implies, highlighter pencils work by reflecting light. That means that whatever area of your face you apply the pencil to, will glow when light hits it. However, if done wrong, the results will be anything but flattering.

Most highlighter pencils will come with their own sharpeners – if not, buy one made for highlighter pencils, to avoid damage. This make-up tool is great to use either as eyeliner or eyeshadow, and comes in different textures.
Sheen highlighter pencils are ideal for a glossy and uniform appearance. This type of pencil diffuses as well as reflects the light, which makes it great for hiding fine lines.
Shimmer highlighter pencils contain tiny reflective particles which give a softer, less pronounced glow.
Glitter highlighters pencils are all about sparkle and act like a shimmer, but with more intensity. When you want more attention, a glitter highlighter will get the job done.
Matte highlighter pencils don't create any shine, but are best for brightening dark areas and are great used as a brow highlighter.

If you want to hide dark spots or dark undereye circles, use the highlighter pencil to lightly draw a few lines over the area. Then pat with your finger to blend. Follow with your foundation. If your eyes are a little close set, draw a line along the top lash with your highlighter and blend the outer third of the line towards the temple. This creates the illusion of greater distance between the eyes. Small eyelids can benefit by applying highlighter to the entire lid. When light hits the eye, the lid will appear larger. Always remember to blend carefully.