The more themes you incorporate, the more creative you will have to be but the process is basically the same. It will also depend how similar or different the themes are. Combining some themes like an Asian theme and Zen theme might be easier than a Zen theme with a rock-star theme. The primary task this is to identify the common consider the living room ideas. For instance, in combing an Asian and Zen theme, you will incorporate a more natural Asian representation like bamboo, jade and the very idea of feng shui. You could also incorporate meditation cushions that would be used in Zen lifestyle and simultaneously represents a classic Asian seating arrangement.