a hamock and a big waterfall.

The first consideration is your location. The secound is your budget and the third is the amount of time you have to spend in your yard each week. Next would be what you prefer. Each person has a different situation to deal with.
Start with a map of your property and a list of your wants and needs. Start filling in your map with the items you desire and work tword those goals.
If your budget is limited, I would start with a seating area and Bar-B-Que. Next would come privacy (if that is a concern). Then any other major piece (a pool for instance). Themes will grow from t Look at garden pictures and decide what you like or dislike about them. Just remember, a place filled with flower beds takes lots of time to mantain.

The design theme I would choose would rely heavily upon the climatic location of my home. It is difficult to grow lush tropical looking plants in an arid environment, for instance. Also, many plants that would provide the ideal tropical environment will not last in a northern climate.
Exactly what ammenities I would choose would depend greatly upon were my yard is located and my home situated.
I would have a Bar-B-Que with counterspace nearby (even if it is something that is stored for the winter). A dinning area or screenhouse (if bitting insects are a problem), would be included as would a comfortable seating area were I could entertain or just have a morning cup of coffee.
A pool would either need to be situated near an accessable bathroom or a cabana built nearby. Outdoor showers are a must in sandy areas to avoid a dirty spa or pool.
Hot tubs are great but in cold winter areas you will need to insulate under it and have a good insulated cover. Getting out of a hot tub into 4″ of snow is an experiance you will not soon forget.
A pond with a waterfall is a must if you have a “natural” theme. Just remember that cold winters will necessitate certain precautions in order not to damage your pond or kill any fish. No goldfish please in any areas that may overflow into a natural stream.
In an arid area I would go with plants that are native and capable of providing shade, and color with a minimum of water. A desert scape with stones and only a small lawn area would do (lawns are water hungry). A southwest theme, Tuscan or Spanish style would work well especally if you provide a varandah or a large grape arbor (or use climbing vines) to add a cool seating area.

A warm southern climate would be ideal for that Hawaian them as would a gazebo. If you live in a wooded area rustic fits in very well. Think about a tire swing to add a touch of nostolgia to the country view.

No mater what theme I chose, I would recommend installing an underground water system to mantain the growth, watering cans are for potted plants only.