For a repair to hold, the damaged area has to be opened up so seed can reach soil, not sit on top of thatch. That usually means raking out the dead material, loosening the surface, putting down seed and starter fertilizer, and covering with a thin layer of compost or topsoil. Then it's water, lightly and often, until the new grass is up and mowed a few times. Expect to keep traffic off the repaired sections for a few weeks and hold off on any weed control, since most pre-emergents will stop your new seed from germinating too. Tell us about anything you've applied recently so we don't waste your money seeding into it. If more than about half the lawn is in bad shape, we'll tell you honestly that a renovation or sod is the better spend rather than patching it piece by piece year after year.