Place a comfortable chair or two on your balcony. While traditional patio furniture will stay in line with an outdoorsy theme, don't be afraid to get out of your comfort zone when it comes to decorating. Consider a wooden bench for your outdoor seating, a lengthy lawn chair or a rocking chair. Opt for seating that is comfortable and appeals to you.
Use a decorative basket on your balcony for things you might use outdoors. Put an umbrella, a favorite pair of outside shoes, a relaxing magazine or a bottle of water inside your basket.
Add a potted plant or flowers to your balcony. Greenery not only improves the appearance of your balcony, but also provides an up-close look at nature. Spring for a traditional pot or consider an unconventional style of pottery if you want something unusual. A vase, an old kitchen pot or even a tin can could double as a pot. Add a bit of paint for more color and a personal touch.
Include some sort of lighting on your sliding door balcony. While you'll likely have light from the large glass door, it's important to include extra outdoor lighting so you can see at night. Place a candle outdoors or an electric lantern for improved outdoor lighting.