The problem with most backboards is that they're much too small for beginners, who end up hitting the ball over every few minutes. Depending on how many balls you have and what's on the other side of the backboard, you can end up spending half your time retrieving balls.
If you lack a good backboard in your area, try to find a nice, high brick or concrete wall (with no windows!) facing a parking lot. You'll get unpredictable bounces off the rougher surface, but having a few stories of height to hit against will often be worth it. Avoid one-story buildings with flat roofs, though, unless you have quite a supply of tennis balls.

