A Realistic Lip Painting Tutorial by Packwood on Deviant Art http://packwood.deviantart.com/art/Lips-Tutorial-V3-375161882 *NOTE, not my art- simply linking so other aspiring artists may use the tutorial for learning. I own no rights. You can use the included link to go to the original page.
I needed this. I don't really like the patronizing from the beginning but it does good in showing the flaws one makes often and more importantly guide us in the way to correct them.Short answer? Observe and practice. Nsio explains: Foreshortening by Nsio on deviantART via PinCG.com