Laying a new sod lawn is not only an exciting experience for most homeowners, but it is also a relatively expensive one, so it is important that your new lawn be given every chance to not only survive, but to thrive. The key to a healthy new sod lawn is in the preparation of the soil before the sod ever arrives. Proper preparation for sod grass takes time and energy, but there is nothing magical about it and nothing that the average homeowner can't do.
Water your existing lawn to encourage the growth of grass and weeds.
Spray your existing lawn with an herbicide seven days after you begin a watering program designed to encourage new growth. Do not water for 24 hours before spraying and do not spray if there is wind or there is the possibility of rain within the next 24 hours.
Wait 14 days for the grass and weeds to die from the herbicide spraying. Use a hard-tinned rake to rake away all of the dead vegetation you can, removing any rocks or other debris at the same time.
Spread 2 inches of organic fertilizer on top of the soil after raking.
Rototill the lawn to a depth of 12 inches, turning the organic fertilizer into the soil so it is well mixed.
Use your rake to level the soil. Water well and use your rake to level a second time if needed. Water your soil well three or four hours before the sod is delivered.
Roll the sod with a lawn roller to ensure that it adheres well to the soil underneath. Water again as per the sod grower's instructions and keep your sod damp but not overly wet for the next 21 days.