If you keep your garden's borders well-groomed, chances are, you're well-acquainted with the string trimmer. A string trimmer either runs on gasoline or electricity. Both styles drive a cutting head that holds a spool of nylon filament string. The string rotates quickly, so it's vital to wear protective clothing like gloves, safety goggles and sturdy boots to operate it safely. Before you start it, clean off dirt and clippings from the deflector using a stick or stiff brush. Drain any remaining fuel into a metal container at least 10 feet away (about 3 meters) from your work area before storing or repairing your string trimmer.