The key to planting new St. Augustine sod is in the soil preparation. If your soil is properly prepared and you water your new sod as per the grower's instructions, then there is practically no reason for your new St. Augustine sod lawn to fail. While the preparation itself is somewhat time consuming, it's not terribly difficult.
Take a sample of your soil to your local agricultural extension office for analysis. (If you are unsure of where to take your soil, consult with a local garden center for directions.) Explain that you wish to plant St. Augustine sod and ask for tests that will help you properly prepare your soil. Such tests are performed for a small fee.
Water your lawn well and encourage the growth of any grass and weeds that are currently growing. After seven days of careful watering, spray all vegetation with a weed killer.
Wait seven days following the spraying of the weed killer. Rake the area to remove the bulk of the dead vegetation and any stones or other debris.
Add the soil amendments that your agricultural extension office recommended when they tested your soil. Make certain that your soil has plenty of phosphorus and iron. Add iron chelate and/or a fertilizer with a high phosphorus content if needed. Add lime as required to bring your soil pH to under 7.5.
Cultivate the amendments into the soil. Cultivate to a depth of at least 6 inches and go down 12 inches if possible. Break up the soil well and mix in all the amendments.
Rake with a hard-tinned steel rake, removing any remaining stones, roots or other debris. Grade your soil so it flows gently away from buildings for proper drainage. Lower the level of your ground approximately half an inch below the edges of sidewalks and lawn sprinkler heads so your new sod will be flush with these areas when laid.
Roll out your new sod onto your well-prepared ground when there is no possibility of frost in your area. Water well, keeping the lawn damp but not soggy for at least two weeks or as per the sod grower's instructions.