When designing your yard, it always helps to have a plan, especially when you are placing items that are not easily moved, such as patios, pathways, large plants, play structures, gazebos, or decks. Drawing your plan on graph paper is usually recommended, but if you would like to do it on your computer, there are several advantages.
Google SketchUp is a free program that can be used to design anything in three dimensions. While at first it doesn't seem easy to use, Google has created several tutorials to get you started. After watching these, you will be acquainted with the tools and should be able to create a model of your yard. You can also save time by importing photos of your location, and create your model from those by using the Match New Photo tool under the Camera menu.
Once your model is created, you can add all the elements that you wish, and move things around until your design is perfect. You can view it from any angle or simulate a "walk-through". Here is my yard plan from various angles:
Once your major elements are included, you will want to plan where to place plants. In order to do this, you will want to know how much sunlight or shade various areas receive. If you have included all the elements in and around your garden, including walls, fences and large trees, this is simple with SketchUp. Simply go to the Window menu, and select Shadows. Check the Display Shadows box, then select your time of year and time of day to see, on your model, where the shadows will be. For this to be accurate, you also need to set your location. Under the Window menu, select Model Info. Select the Location option, and set your location by city or latitude. This is also where you can reposition north on your model. Here is where the shade is in my yard in the middle of the day on June 21st:
Unfortunately, unless you buy the Pro version, your model won't automatically generate a blueprint-type plan for you to work from. However, it is simple for you to add the measurements yourself and create a plan to work from, like this:
There are several programs available online to help you plan your garden that will do a better job of placing specific plants. But for designing your overall landscape, SketchUp is a great program with many helpful tools, and best of all, it's free!