Set mower to the highest setting. For lawn grasses grown in Maine, the best maintained height is 3.5 - 4 inches or the highest setting on your mower.
Mow frequently. Be sure you never remove more than 1/3rd of the leaf blade. Cutting more shocks and weakens each grass plant.
Leave clippings on lawn. They provide free turf food and are best left on the lawn. Mow when grass is dry, preferably between the late afternoon and before the evening dew. Collect and remove clippings only when they are visibly heavy.
Keep those mower blades sharp. Sharp blades produce a clean, uniform cut. They also limit damage to the leaf blade, reducing water loss and opportunities for fungal disease infection. Sharpen after 7 - 10 hours of mowing time.
Vary your mowing pattern. This reduces soil compaction and scalping which in turn reduces weed invasion.