I always thought unicorns were skittish creatures. I like the way Ridley Scott did it in Legend. I'd put the girl on one knee reaching up. If you put the unicorn a little higher up it will also not look like he is about to take a dip. It looks like sunset and the mountains are dark but the fog and the foreground are in bright day. If you put a lantern or maybe some floating lanterns in the lake you could explain why the figures are lit. You could also loose some of the fog and make the light a ring. As it is now the fog pulls the focus off the characters. Now for the technical comments. The wings on the unicorn are too high up, almost coming out of the neck. Move them down to were the shoulder muscles would be. The girl's bell sleeve should be hanging down flat on the arm not floating 4 inches above her wrist. You will probably have to go into poser and pose the dress seperately to fix this. Bryce trees have those fat little bulges in the trunks. Sink them down further into the ground and scale or whatever to hide them.