Reseed your lawn in spring. Begin by looking for dead grass and for spots that have winter or grub damage. Remove debris like dead grass by raking, and topdress the area with peat and topsoil.
If reseeding spots killed by grubs, apply a grub insecticide, and wait a week or two before reseeding. Apply a starter fertilizer at the time of seeding to help the young grass grow. Mulch the area, and keep the ground moist, even if you must water it more than once a day. Do not use herbicides on the reseeded lawn, and wait at least three weeks before mowing it.