Maintaining a lawn and Sandy soil is very challenging as you probably know. In order to have a thicker lawn the lawn will need water frequently because sandy soil dries out so quickly. It will also be cost-effective to allow the lawn grass to set seed in the spring. Resist the urge to mow early in the spring so your grass develops deep roots. Keep it at a height of 3-4 inches so it shades it’s own roots and retains more moisture. Only cut off 1/2 inch at a time. Hard to do for some, like my husband https://turf.umn.edu/news/finding-right-grass-seed

https://extension.umn.edu/lawns-and-landscapes/lawn-care