OKay: Mane, tail, fetlock hairs need transparency maps. This way it looks like you cut him out of somewhere and pasted into the pic. Actually, both of them look like they are pasted. No shadows anywhere! Too high ambience? So, the figures should interact more with the background. That's the main reason picture doesn't look good. Maybe you should increase the size of everything and use camera view. Then, play with magnets on her clothes. Yep. Too stiff and unnatural. Then, yes, the unicorn has to be bigger. It's a bloody big horse with a horn, so make him rear above her. I think there's a Poser pose either inside the program library or somewhere among free stuff. Then, you possibly used a cloud plane for mist? Something like that is visible on the tree trunks. Use spheres. Then, either use mountains or use sky for the background. These mountains are simply not big enough in combination with everything else. Then, the colours of lotus leaves and the rushes and the tree leaves are simply wrong. BTW, the tree leaves are too big for those trunks. Use size 1 or 2, and increase the quantity. Composition wise, it's not exactly that the pic doesn't follow the golden rule... It's that the composition is too flat and static. Put them on a diagonal. Finally, if this is the final side ratio, it's one weird book format. Anyways, you need space with pretty neutral background for the title and authors and so on.

-- erlik