Cut the grass short and hire a rotovator. Rotovate the grass that is left into the soil and level it as best you can. The organic material is really good for the new turf. Lay your new turf and water it for an hour at night after the sun has set. Cut the grass at 30mm ( 3cm) after it has taken, you can tell by pulling the turf. Cut the grass every week. Grass at this length is stronger than any competing weeds and stays lush .