One of the biggest things people neglect to take care of prior to aeration and seeding is killing the weeds. I am mainly referring to crabgrass. Crabgrass is the biggest killer of grass. Crabgrass has developed high tolerances to heat, and needs little water to thrive. It is truly the only thing growing when everything else is brunt up. This allows for the crabgrass to spread and take over new areas of the yard. Grass that has been chocked out or pushed out of the way by crabgrass will not be able to return on its' own. Spraying to kill the crabgrass at the root is the best, then rake out all dead areas left behind by the crabgrass. Afterwards you will notice bald and bare areas where the crabgrass once was. Make sure to till these areas good and incorporate grass seed and maybe extra topsoil or compost to help level off the area. Don't forget to water!