All debris from building should be removed from the site and evaluation of the remaining soil can be taken at this time. The first phase in planning should be a soil test. This will take a few days and while you are waiting you need to get the prospective lawn in shape. Water logged lawns are just as bad and drainage needs to be installed before the lawn. Many grasses will not take standing in water and need well draining soils to grow.
Poor drainage can lead to fungi and diseases setting in.
You may need to fill in some areas or do some creative landscaping around these areas. All areas that are to be incorporated into the mown part of the lawn need to be as debris free and the ground as smooth and even as possible. Pieces of wood will decay and soft areas will often begin to sink later if not taken care of in the beginning. Lawn Grasses - Weeds and more. Depending upon the time of year you ca also get rid of the weed problems that arise later.