You can read every treatise on figure painting ever written, but until you sit down and put paint to plastic/resin/metal you won't get very far. As ajlafleche said "practice". The more you do, the better you'll get. You will fail, you will suck, you will quit, you will strip paint, repaint, cry, scream, and then one day you will hit on the technique, timing, materials that you sit back and look at your piece and you'll be happy. You'll feel better and once you have these little victories you'll try newer and bigger figures. Soon, you'll be missing paying the bills to buy paint and figures, sell the house, skip meals, friends will knock on your door with no answer because you'll be at your work bench with a grey army at your beck and call. Romans, Goths, Napoleonics, Medieval, ACW, ECW, WW2, all will be there on your desk waiting for paint. You'll be hooked. The guys at Warriors, Verlinden, Alpine, Dragon, Pegaso, Seil, Andrea will be wringing their hands like a pimp at a Shriners convention. When its all said and done, and you find yourself on the bathroom floor at the World Expo or at Euro Militaire and you are destitute, unshaven, underweight and stroking Pegasos newest release, then you'll be a figure painter. At least until someone comes in and says "Man, did you see those new injection molded armor kits?"
Hit some of the shows and hang around the figure entries. ASk questions, look at techniques, you'll be amazed what you can see and pick up by being able to see the actual figure. The stuff reproduced in the books looks good and looks like there is more there than actually is. I've seen guys that in the books I thought they wer into some insane detail, until I saw their pieces in person. While good, I was able to see that they make the illusion of more detail and do wonders with paint and color.
The other thing, is to do some pieces and put some pics here on the forum. The more you are open to criticism both constructive and critical, the better you'll become. While not the same as sitting at the bench, there are some very talented figure painters here that can offer some very good advice and help you along. Most importantly remember a few things.
Don't let your expectations exceed your abilities.
Be open to criticism, retain what you think is helpful, disregard the stuff you don't think you need or that is just bs or someone being stupid.
That with practice and the willingnes to try new things you'll advance faster than if you were worried about final results and what others might perceive of your work. Are you painting for you, or us?
Don't be too critical of yourself, you are your worst critic.
If you can, look for quality figures with clean and crisp detail. You are not going to get the same results with Tamiya figures from circa 1975 molds that you would with a Warriors, Apine, Fonderie or Verlinden. The extra money is worth the investment for the better figure. If you have a better foundation to start, you'll have an easier and better result from your work.
Be willing to strip and clean a figure and start over. Not everyone will be a home run. Expect failure, accidents or that your experiment or new technique isn't working. Its why we experiment.
Don't be afraid to ask questions. There are no trade secrets. No secret recipes. This is a talent based hobby and you develop talent. There is no clinical proof that humans retain racial memory. You may have an aptitude for it, but you must develop skill. Others have gone before you and invented the wheel. Ask them. The only dumb question is the one you don't ask that keeps you baffled. You will be surprised how much you will pick up by listening to others tricks.
Enjoy it. If you're grinding your teeth at night over a figure, try fly fishing.
Mike