From How Important Is a Perfect Lawn When You’re Selling Your Home? [New York Times 2014-08-06]:
“The simplest way to not screw up your lawn is to set your mower as high as it will go and make sure your mower blade is very sharp, so you’re cutting the grass blade, not tearing it. When you cut it lower, the grass doesn’t have the leaf material to do the photosynthesis that it needs to sustain itself. … The best time to take care of our lawns in northern climates is in the fall: Labor Day to Halloween. Any grass seed you put down at that time should do fairly well.”