Tutorial on Photorealism for unity games?

I have a scene with a horse and a barn and it looks cartoony -- like an amateur 3d game. How do I go about making it look more photorealistic? Are there tutorials on this someone can point me to. I've seen some beautiful renderings in games but haven't seen any step by step on how to achieve anything like that. I've watched the unity tutorials already but their demo scenes look good to begin with which make me think that it may not be possible given my current textures maybe aren't so hot. Are there some resources for making games look better?