Visualize the path in your mind. Before you begin to give directions, play an imaginary movie of the user's route in your mind. By "walking" yourself through this practice route as you dictate the directions, you will be able to get the user to exactly where he wants to go.
Start from where the person is standing/driving right now. Tell him to "turn left immediately when leaving the parking lot," instead of starting your instructions at some point farther down the road. Starting where the person is located will assist those who are not familiar with any of their surroundings.
Limit the number of steps required. You may know of a local's shortcut to the location, but if that route takes too many steps to explain, you will not save the person any time. Instead, try to limit the number of steps (or turns) required to four or fewer. If the route is more complicated than four steps, you may need to draw the person a simple street or landmark map to work in conjunction with your directions.
Explain the directions from the person's point of view. Try to avoid cardinal directions (north, south, east, west) if possible. Instead, consider the person's point of reference and use "left" and "right" instead. Give as many visual landmarks as you can, preferably one at each turning point.
Provide a visual cue for the destination. If there is a visual landmark that can be seen from a distance, mention it. If the person forgets a step in your directions, she will still be able to see the "giant golden dome" of the capitol building from many blocks away. As long as she is closer to her final destination she can always ask for updated directions.
