John Drengenberg with Underwriters Labs says don't mow when the grass is wet.
"When the grass is wet, you could easily slip and the lawnmower could slide back over your foot and this could cause a very serious injury," he says.
This is why you should never mow when you are barefoot or wearing sandals. It's best to have a very solid shoe, just in case.
Make sure there are no kids or pets around when you're mowing.
"Because very often debris and stones could be thrown by the lawnmower and could injure someone who is close by," says Drengenberg.
Be especially careful if you need to work on the mower, whether it's to sharpen the blade or remove debris.
""Be sure to disconnect the spark plug from your gasoline-powered lawn mower before you tip it over and start working on the bottom," he says.
With an electric mower, make sure it's unplugged.
Never start a gasoline-powered lawn mower in the garage. You don't want the carbon monoxide to build up and possibly seep into the house.
More Information: Consumer Product Safety Commission: Lawn Mower Safety