i don't know how many teen girls pluck say their upper lip so there's no hair (personally, i do)...
but i've found that you should wash your face with warm water and a gentle soap made for sensitive skin first. then pat your skin dry, apply a medium-thickness moisturizer to your face, then hold your skin taught with the palms of your hands while you pluck the hairs.
it's easiest to find what hair you want to remove when you have a magnifying mirror - it also prevents you from going to far.
there's less pain in plucking your upper lip then plucking around your eyebrows, but once you get used to it you stop recognizing that hurts.
i hope i could be of help!
Adie.