Look at your site. What if anything is growing there? Try to identify the problems. Are there invasive weed species. Is area prone to water logging?
Usually, it is better to work with soil you have and improve it by addition of leaves, compost, manure grass clippings and any other organic matter you can source. Bringing in topsoil is always a risk.
It is possible to plant without any preparation into fresh topsoil, or lawn but prepare to hand weed intensively for two years if you do.
Mulching after planting with grass clippings or bark mulch or leaves will help smother emerging weeds but the demons, scutch grass, bindweed, ground elder, nettles and creeping thistle will push through most mulches and will have to be hand pulled.
A one-off spray of the toxic herbicide roundup will kill all really invasive species like bindweed, scutch grass, nettles or creeping thistle if applied at the right time.
Covering ground with black plastic or the woven black material mypex for six months will work but can be difficult to pin down.
Laying out mypex and planting though holes cut in the material is more expensive and more difficult but it will work. Long-term, it is not healthy for the plant roots. It kills all the beneficial bacteria earthworms and insects in the soil and stops the natural process where old leaves fall to the ground, decay and provide nutrients for the hedge from which they have fallen.
