Personally, I don't like the look of applying it outside the natural lip line. It's always very obviously fake to me.
So, I would suggest applying it inside the natural lip line.
Also, put on a little lip balm first, as that will make it glide on easier. Then, after outlining, fill the lips in with the liner as well. This way, when your lipstick/gloss fades, you'll still have color on the inside of your lips, instead of just an obvious outline. If that makes any sense.