Hmm, maybe drag the lower wing tip richt in the sand, creat a small trough and some sand spray. Go with a gray for the smaoke, I agree ditch the camels they really do not add anything to the scene. If you tell me where you got the modle from I could make up a nice bump map for the aircraft skin to kick up the render a notch. A little more propellor blurring would also help. The smoke should origonate from the exhaust stacks on either side of the nose. Who cares if it obscures the model a bit. Possibly a bit too yellow try more of a tan, Let the scene be colored more by the texture colors not the sun lighting, I know tough to say without having the scene open infront of you. alot of input? Well you asked.