The better prepared your soil is, the better your turf will perform.
1st - Get rid of any existing weeds and grasses, using a weed and grass killer. Follow package directions.
2nd - Rototill soil so that you have a minimum of 2 inches of good, loose top soil (4" to 6" is ideal).
3rd - Soil test your lawn. See your area County Extension agent for information on how to test your lawn. You may need to add lime, peat or compost as recommended.
4th - Rake and smooth soil, removing rocks, roots and large clods. Keep the grade 1" below sidewalks, driveway, etc.