There are some wonderful lighting sets in Free Stuff that have helped me tremendously, but the coolest set I've found was Blackhearted's Pro Luma Light Set, which cost amazingly little in the Marketplace. It may even have been the first thing I purchased there. Once you find a setup you like, see how well you can duplicate it on your own, starting with one light. It's working for me :) Illustrender sets by SnowSultan are excellent, too--I think I've collected all of them (and they're free). Good lighting seems to make the difference between life-like and plastic people in Poser.