Mixing patterns is a dangerous game, with hopefully beautiful results. It may be tempting to put a floral rug next to a Navajo tapestry, and you may equally like both parts, but consider the disjointed effect it gives. If you plan on mixing patterns, keep within a similar color palette and the thickness of the lines. Also, think of it in terms of sizes. A crazy, awesomely patterned rug should be a statement piece, and while a cool designed accent wall may look amazing, maybe it'd be better to pair that rug with a couple of interesting throw pillows.