Visibility - Decide how visible you want the wall sticker to be. It you are proud of it and want people to take notice place it somewhere with high visibility like the living room on an adjacent wall from the television so there is more coverage. Essentially any place that does not have furniture near it will lend high visibility. If you don't care either way, place it where your heart desires.
Using Furniture - Use your furniture as a prop to the wall sticker. This can get creative and fun, too. Using furniture as a prop take a little more creative genius but there's nothing wrong with trying to tap that while looking for a wall sticker. Consider the color of your furniture, what message you're trying to convey and how "loud" you want the decal to be. Floral and sky designs work best with furniture like chairs and sofas. Vertical scenery works well near lamps and entertainment centers.
Use More than One - It's okay to buy more than one package that is more than one design. Create a story out of it and if anything else, get as crazy as you want because it's your creative genius at work. It doesn't even have to make sense. You can have Paris being overtaken by flowers or you can have a cat playing with a Disney character. The possibilities are endless.