To be dense and healthy, your lawn needs a certain amount of sunlight daily. Some grasses are more shade tolerant than others. Be sure to choose a seed mix that is suitable for your sunny conditions. If you don't get any sun at all, it's better to choose a different plant. For shaded areas, choose seeding rather than sod, which is mainly composed of Kentucky bluegrass, a grass that requires sun. Choose mixes of more tolerant varieties such as fescue or ryegrass. Annual overseeding can help you increase the density of your lawn, even in areas where it is difficult for lawns to grow.