Here are a few quick pointers on planting grass seed.
Ground Prep: When putting down grass seed in larger areas it is best to use a tiller or ground rake to break up the top two inches of soil. This helps the grass seed germinate in easily permeable soil which will increase the root depth of your new turf. If your newly germinated grass has deeper roots it will last longer during hot dry times of the year.
Topsoil: Using bagged topsoil when spot seeding is acceptable but it is still best to break up the existing ground first to avoid runoff and help with root establishment.
Reminder: Use an overseeder or garden rake to make grooves in the ground that run perpendicular to the slope of the ground. Drop the seed in these grooves and rake approximately one fourth of an inch of dirt over the seed. This will help the seed stay put during periods of heavy rain. Lightly cover with straw if desired.