STEPS:
Line the perimeter as you typically would.
Now start filling in the inside two-thirds of the way in. Note: I like to leave the inner third bare so it creates a little illusion of depth = fuller lips. But you can certainly fill in the entire lip!
Then finish with a coat of lipstick using a lip brush for precision or straight from the tube for convenience.
This way, as time wears on and the lipstick wears off, you have less of a “line” left over!
Note: I exaggerated her lip perimeter slightly for photographic purposes.