Make a list of everything you want to use the backyard for. Prioritize the list, with the most important uses at the top. These top priority uses should get the most space. Some examples of uses are patio, rock garden, relaxation, recreation, pets, home environmental protection, guest intertainment, fruit and vegetable production, and flower garden. Make a detailed scaled drawing of your backyard including all obstructions and corners. Draw in to exact measurement, the different types of landscaping you desire.
Consider how the sun moves through the back yard through the seasons. In the northern hemisphere, if your back yard faces east, you'll get morning sun and afternoon shade. If it faces north, it will be cold and shady most of the year, because the hoouse will block the sun most of the time, except mid-summer. The opposite is true if it faces west or south. The south side will get sun year around. The west side will get morning shade and afternoon sun. You typically do not need shade trees on the north and east sides of the house. However, a shade tree on the south or west sides would keep the house cooler in the summer. If it is a winter dormant tree, it will drop it's leaves (called deciduous) in the winter, allowing sun to hit the house and keep it warmer (known as solar gain).
Take a took at some of our back yard landscaping ideas photographs in a slideshow.
Another consideration is property soil type. Depending on where you are in the watershed, you may have rocky, sandy, or clay type soils. Typically, higher elevation properties will have rocky soils, because the smaller material washes to lowers elevations. Rocky soils drain the fastest, followed by sand. Clay type soils hold water for long periods of time. You can grow more drought tolerant plants in rocky and sandy soils, and plants with higher water needs in clay soils.
Evaluate your placements and redraw if necessary. It's best to make your mistakes before doing the actual work. Make sure to include pathways and irrigation routing in the drawing.