I use them just like any other lipliner from the perm line: Prep my lips, then line (and fill in, if you like), then apply a lipstick and gloss on top. If you want to skip the lipstick, you can just line with the lipglass pencil, then proceed to apply gloss directly on top.
They are sheerer, smoother (or slippery), and a lot softer than regular pencils though - and I find they get used up a lot quicker because of the consistency - that's the only thing I don't quite like about them