Grass requires several things to grow well, including nutrition, proper drainage and water. Soil that is very sandy can be a challenge to grow grass in because it has such good drainage that water may not stay near the grass roots long enough. Sand also lacks nutrients the grass can draw upon. You will likely need to amend the soil if you want grass to grow well in significantly sandy areas. Slightly sandy soil will likely not need amending, as this is ideal for grass.
Aerate the lawn with a mechanical or hand aerator. Run the aerator over the entire area on which you want to plant grass. This will create channels for added organic matter to work into the soil.
Mix loam or topsoil with peat moss or compost. Mix the two in roughly equal parts to get a crumbly, loose soil that is not too heavy.
Amend the soil by topdressing it with compost. Do this in spring or early fall to give the compost time to settle. Spread the topsoil and compost over the entire lawn in small mounds, a few shovelfuls for each square yard.
Work the topdressing mixture into the soil with a garden rake. This can be done over existing grass or bare ground. Use the back and tines of the rake to spread the topdressing over bare spots or depressions, and work it well into the aeration holes.
Water immediately afterward. Let the topdressing settle for a day before going out and smoothing it down again to make up for any runoff or hollows that occur.
Use a grass seed that is suited to sandy soil. Try fescue in cool-season climates and zoysia or Bermuda grass in warm-season climates. If you have existing grass, you can use these to overseed the lawn after applying the topdressing.
Water new grass seed daily for the first month to ensure good germination and be sure the grass is getting the water that it may lose quickly in sandy soil. Water in the mornings so the grass gets a chance to use it before the sun evaporates it. Once the lawn is established, water every other day or every few days, depending on rainfall.
Add fertilizer lightly and regularly. Use a high-nitrogen fertilizer to make up for the nutrients the sand lacks. Do another round of compost topdressing in midsummer to build up the soil and give the grass a growth boost.