Go to Wal-Mart and buy some painters tape and toothpicks. If you want to paint a curvy line, apply tape and scrub the seam with a toothpick or something else that is soft, then use a razor to peel it off and paint away once you get it firmly adhered into the crease. Thin your paints to the level of water, and try your best to do as many coats as possible if you're doing more than just dabbing paint onto chipped spots. Use a magnifying glass / jeweler's lens and you will be much happier. Buy a cheap brush from Michael's but better yet buy a $5 pack of 2-3 sable brushes and make sure they're very small. If you want to have longer to work on your paintjob, thin with distilled water, if you don't need as long, use high % alcohol. Shake your paints, a lot. Don't be afraid to try and paint it, if you're unhappy simply use a wet lint free cloth and wipe it off. Generally if you can't get a good 1:1 match on color, just get it close and paint a larger piece.
Oh well I will probably get shit on for trying to help.
t. model fag