A couple of methods for prep are:
Cultivating Unwanted Plants
Any soil disturbance is followed by more weed growth, so cultivation needs to persist through an entire growing season. Stubborn weeds may require two seasons and some deep-rooted rhizomatous weeds, like Canada thistle, may not yield to cultivation.
Weeding with hand tools is best suited to small areas. For larger areas, cultivating with conventional farm machinery can be an effective way to eliminate established perennial weeds from rich, heavy soils. If your large site was previously a cropped farm field (therefore free of perennial weeds) or if it contains deep sand or gravel soils that do not support heavy weed growth, several diskings prior to sowing seed may be all the cultivation needed.
For more common, weed-prone soils, cultivation of large sites should begin with fall plowing. If the soil is subject to erosion, however, defer the initial plowing until spring. When soil can be worked the following spring, cultivate with a disk to a depth of four to five inches. Cultivate every two weeks until fall in an effort to destroy the roots of perennial weeds.
For quack grass or other rhizomatous species, follow the initial disking with a spring-tooth harrow or digger to bring roots to the soil surface, where sunlight and drying will kill them. After all weed roots are dead, switch to shallow cultivations timed to eliminate freshly germinated weed seedlings.
Repeated shallow cultivations one or two inches deep through two growing seasons can deplete the shallow weed seed bank without exposing weed seeds from deeper in the soil.
If you are planting your large site to native species in the fall, use a harrow or drag to produce a smooth, clod-free seed bed. If your soil is subject to erosion, consider deferring your planting until spring and first plant a winter cover crop in the fall. In spring, several shallow cultivations will eliminate the winter cover crop and any freshly germinated weeds. After a final dragging, the soil will be ready to plant.
Smothering Nuisance Plants
For preparing sites smaller than a few thousand square feet, smothering weeds can be effective. It is a simple technique that requires no chemicals or special equipment.
The idea behind smothering is simple: A plant can’t live without sunlight, so covering the soil surface for a full growing season will kill the unwanted plants underneath. Some weeds need to be covered for two years. Smothering a lawn takes less time; usually it can be killed in two months by a close mowing before covering.
Black plastic is a common choice for a smothering material, but it has a tendency to deteriorate over time. It may blow away if not properly anchored and can be punctured by sharp weed debris left underneath.
More economical choices might be salvaged or recycled wood paneling or industrial-weight tarps. Other suitable materials include newspapers or cardboard covered with leaves or grass clippings. Old carpeting works, too, but if left too long can decay and become difficult to remove. While smothering will eliminate plants, a large weed seed bank may remain.