Having a deck can be great. However, for those of us who have never had a deck before, figuring out how we want to decorate or use the space (besides just for grilling) may be a bit intimidating. Here are a few ideas to get you thinking about what you would like to do.
Design - For the base of the area think neutral tones. It is an "outdoor room" in a lot of ways, but, you want it too look like it all belongs outdoors. If you have a good, neutral color palette with a pop of color here and there, then it will feel natural and relaxing.
Decor - When considering your main decor, think simple lines and low lying furniture. This will also give a relaxed, comfy feel as well as not block your line of vision. The bigger a piece and the taller, the more it seems to take up space. A deck is for lounging, so keep that in mind. Also, unlike a porch, a deck may or may not have a roof or a cover over the area. Maybe have at least one area with an umbrella or furniture piece where there is some relief from the sun would be nice.
Duty - Keep your outdoor accessories leaning towards function more so than form. Having a ton of little things just to "look nice" will clutter the space and take away from the peaceful vibe you need to have on a deck. Have places to hold drinks or plates and maybe some potted plants for color, but, don't over do it. This also makes it easier to keep damage away if you have less to protect when a summer storm hits.
Decking Care - When you are cleaning a wood deck use a mild oil-base soap with warm water. Sealing it yearly (or bi-yearly depending) will help keep it protected. If you have a PVC deck, warm, soapy water or a good power wash will keep it in pristine shape. During the summer season, generally sweeping it every so often keeps it nice and ready for entertaining--whether just for yourself or others!
So get outside and enjoy the deck! You will be glad you did.