Once you have chosen and cleared the entire site, considering downhill gravity and drainage issues on the land itself, you can begin laying out your plan. Whether mortared or dry-stone, it's essential to define exactly what you want: how long the wall will be, how thick, how corners and gates will work, and so on.
Be exacting. A big part of the project is going to be making sure your decisions stay stable; for example, what if your plumb line weren't kept taut, and curved in the wind? You could end up building to what you think is a straight line, and end up with a bizarrely curved wall that'll eventually tear itself apart. On the other hand, if you want a curved wall, think about laying out a garden hose or similarly thick rope to plan the trench that will hold your first course of stone, then build the shape into the wall as you work.
While planning, keep a few rules of thumb in mind: Firstly, there is a huge difference between walls taller than 3 feet (0.9 meters) and walls that are shorter than that. While the base of a shorter wall should be equal to its height, anything higher than 3 feet (0.9 meters) requires an extra 8 inches (20 centimeters) in width for each foot of height. Therefore, a 3-foot (0.9-meter) wall has a 3-foot (0.9-meter) base, but a 7-foot (2.1 meter) wall needs a base of no less than 4.6 feet (1.4 meters) [source: Vivian].
The appeal of stone walling is its permanence: Half the task is keeping that in mind. The higher the wall, for example, the deeper you should sink it. For anything higher than waist level, you should dig your trench at least 2 feet (61 centimeters) -- or deeper, depending on the frost line for your particular region. (Frost forming and thawing will cause your wall to move up and down, but if your dry rock wall is sunk into the ground, that moisture can pass through the small openings in your structure.) On the other hand, for a shorter wall you need only worry about sinking it by 8 inches (20 centimeters) or so: Gravity will do the rest, as the wall figures itself out [source: Volk].