When preparing your area for a new lawn make sure the area is free-draining and remove all weeds and vegetation.
Remove the existing vegetation.
Spray your lawn with a weed killer as per the manufacturer’s recommendations, wait for the old lawn to die, then rake away the dead vegetation. Do not lay your lawn over existing grass.
Preparing your soil
Test your soils PH. For acidic soils add lime (PH below 6). For heavy clay soils add gypsum. These are available from any good garden suppliers.
Rotary hoe or dig the soil to a depth of 100-150mm. You may add loam topsoil; if you don’t, make sure your existing soil is friable. Rake the soil level and prepare a firm surface for laying.
A wetting agent can also be applied to assist in water retention. If you are installing a sprinkler system, do so after soil preparation. Water the area to settle the soil and provide a moist base for laying the instant lawn.