Soil preparation consists of killing all weeds, and making sure the soil is suitable for growing a lawn.
There is a temptation to buy new topsoil, but unless you really do require more soil, it is better to improve and treat what you have.
The reason for this is simple, you will probably buy soil which is just as bad, if not worse than what you already have.

We have products that will improve the quality of your soil.

Clay breaker, pH correction, Under tree dress, Lawn reviver