Incorporate textures like suede, adobe, and denim in fabric or wall paint, cowhide rugs, stitched patterns. Think sturdy, wooden furniture, overhead beams as in a barn/farmhouse, horse keeping supplies displayed.
If you're trying to decorate with a "Western" feel, cowboy hats and boots, horses and even guns will go with your theme. Think of Western movies and things that you can use from them to decorate and you should be able to master the Western decoration theme that you're going for.
