Preparing your soil for turf.
Spray the area where the turf will be laid with Roundup. Wait at least a week to make sure all weeds are dead. If you have a good quality top soil, with good depth, you are lucky. This will quite likely be compacted though, so you will need to aerate (rotary hoe) the soil.
If your soil is clay-like, you will want to dig up the soil with a rotary hoe. Be sure to spray for weeds beforehand and spread in gypsum to help break it up. You will then need at least 10cm, ideally 15cm, of quality sandy loam spread on top.
Although your prepared soil may look weed free, there is always the possibility of weed seeds germinating after your new lawn has been laid, as seeds germinate at different times of the year.