I love the colours you've chosen for this image! They're so...dreamy and soothing. Very nice. The clouds look fine to me, but if you'd like, here's a link to a tutorial: http://www.epilogue.net/art/tech/socar_clouds (it's for Photoshop, but maybe you can learn a thing or two from it anyway). Sorry I can't help more! I've been trying to draw realistic clouds for two years now, and am still going nowhere...sigh!
Anyway, this picture is very well done, especially for only a third time working with Painter (not the most user-friendly program, I know). Keep up the good work! :)
I can feel the freedom this dragon is experiencing just looking at this picture. Couple minor critiques, its arms are a little skinny and the leg shields seem kinda out of place somehow. Minor problems, though, the shading is beautiful and the cloud streaks are a nice touch. Afraid I can't offer advice on realistic clouds, since I don't know how to do 'em myself. Lovely picture, anyway.