I have thin lips too. For me, I have found that they look best in lighter colors and MLBB as opposed to dark colors. Sheers and glossy finishes look best.
When I do wear dark lipstick, I take pains to apply it well, because my skin is very pale, and the lipstick is very high contrast with my skin. I use the following technique, which I think I learned from some Lisa Eldridge videos:
I exfoliate my lips to start (I use EcoLips, but anything similar will do), and then I apply a bit of lip balm and let it sink in while I start the makeup for the rest of my face. When it's time to do the lips, I wipe off any excess lip balm and then prime with Urban Decay Ozone. I then put on a very thin coat of lipstick (it can be kind of messy) and then use a lip pencil to clean up the edges and to overline my lips a bit (my upper lip is thinner than my bottom one). I blot and then apply a second thin layer, usually with a lip brush. I then blot again, this time putting some translucent powder through the tissue (I use only one ply of the tissue). I then apply one last coat of lipstick to finish.
I rub my lips together quite a bit during the process to really work the lip color in.
I find dark lipstick a lot of work to apply well (as noted!). I think that liquid lipsticks are easier if you want to wear dark lipstick, because the edges are cleaner and the liquid lipsticks usually don't fade or bleed as much. The downside is that they are generally pretty drying.
For liquid lipsticks, the ones I like the most are from Stila, Anastasia, and Too Faced. For regular lipsticks, I like Urban Decay best. If you want to try a matte, Urban Decay has something called Comfort Matte that isn't so drying.
I would highly recommend going to some kind of larger makeup store, or the makeup department of a higher-end department store, and have the staff make recommendations for you. Most of my favorite colors were purchased because a consultant recommended something; I would never have found them myself. I also try to go to a store that has an abundance of natural light so that I can see right away the true color of the lipstick on my face.