I do the Integratated Pest Management (IPM) route touched on by Kestas. Keep your lawn reasonably healthy, use low to moderate amounts of nutrient addition, and only use pesticides when pests (weeds,insects,disease) reach a threshold, either impending or already there. It's good to do a soil test to know where the pH and nutrient levels are and management can be done if required. In Michigan, it is usually not good to apply N before the grass has started to grow. The roots are full of nutrients stored from last fall and early N encourages over growth in spring, which is not healthy for the grass and encourages disease. Fertilize after that first heavy growth is over - after several mowings. And, return all the clipping nutrients back to the soil. Use a good slow release fertilizer or some of the organic products if that is your choice. Don't fertilizer through mid summer if you don't irrigate. Let the lawn go dormant. Fertilize again in early fall when the grass is storing nutrients for the next year. My goal is to keep the lawn reasonably healthy to avoid getting into that high fertilizer/pesticide regime. That means I tolerate some imperfection: weeds, etc..