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Ensure the lawn's edges have been trimmed using equipment such as a weed eater. Mow in rows or columns. Set your mower height. Make two passes across the lawn to catch any missed areas.

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Not only will trimming edges make the lawn look more professionally mowed, it also will establish a perimeter so when you start mowing you can better see where you need to go. Be sure to cut the grass around flower beds, trees, and any areas the mower is unable to reach at approximately the same height as you set the mower. Be careful not to damage the bark at the base of the trees, don't cut the grass too low, and definitely don't chop anyone's prized petunias. Be sure and mow from one edge  all the way to the other before turning around. Creating zig-zags or missing spots of grass will look unprofessional. Different types of grass require different heights of cut for a professional appearance. Identify the type of grass before you set your mower height. Remember to alternate the mowing direction each time. If you don't alternate the direction you can cause excessive wear or even damage the lawn.