Read the owner's manual carefully. Be sure electric units are either double insulated or connected to a 3-prong grounded outlet. Use a properly sized outdoor type extension cord for electric units. Do not use electrical powered units in damp or wet conditions. Be sure the working area is free of hazards, which could hamper the use of the trimmer.
Trimmers can throw objects with force so keep children, bystanders, and pets from the working area.
Keep the trimmer close but not touching the ground. Angle the unit slightly to the left to discharge trimmings away from your body. Hold the trimmer firmly with both hands in a properly balanced stance. Keep the hot engine and exhaust away from your body. Use only monofilament string recommended by the manufacturer.