Attached Link: http://www.3drender.com/light/index.html

You may slap me for this, but your image is underexposed now. It's dark and lacks contrast, and overall looks murky. If you take a look at the histogram, you can see that you're only using half of the tones available. A really great resource for lighting advice is the book "Digital Lighting and Rendering" by Jeremy Birn. It's available at Amazon.com, and I saw the other day that Poser Pros is selling it as well. (Personally, I thought the section on key-to-fill ratios was worth the price of the book alone, because that's the first time I'd had it explained to me.) The author has the first chapter as well as some other useful information on his website, including a tutorial on 3-point lighting.