Remove existing grass or weeds, if necessary. Apply a herbicide such as Roundup or a similar product to kill the existing grass or weeds. Apply a second application, if needed. After most of the grass or weeds have turned brown, use a rake to remove the dead grass.
Take a sample of soil to a local extension office or professional for testing. The soil will be tested for pH and other elements. Add lime or other nutrients to improve soil fertility as needed.
Loosen soil and mix in lime and other nutrients using a rototiller.
Install an irrigation system if there is not a existing system. This will make it easier to water new sod once it has been laid.
Fill in trenches from installation of irrigation system with soil. Level ground with a rake or shovel to remove high areas and to fill in low areas. Remove any remaining roots, rocks and other debris from the soil.