There are two simple rules that you can follow to maintain a beautiful lawn. The first is to sharpen your mower blades. Having sharp blades will cut leaves rather than tearing them. This will reduce disease pressure and the lawn will look a lot nicer. If your yard is like mine and you have mole hills you may need to sharpen your blades a couple of time throughout the season.
The second rule is to keep the mower deck two to two and a half inches off the ground. Once the seed heads are removed from the grass in May, raise the deck another half an inch. When we mow too close, the grass is weakened and allows weeds to complete more easily in the lawn. By mowing higher and removing no more than half the grass, root development will not stop, there will be move cover to soak in the rain, the soil will stay cooler, and weeds will be at a disadvantage.
Source: Garth Ruff, OSU Field Specialist