The most important part of lawn maintenance is to have a sharp mower blade. As the blade dulls it starts to tear the grass blades instead of cutting clean. You can see this happening if the tips of the grass blades turn yellow or brown.
For those of us who own mulching mowers, it is very important to keep the blade sharp. The blades re-cut over an over until a fine "mulch" is returned to the lawn for fertilizer.