The methods for restoring a prairie depend greatly on your starting point. If you are starting with a remnant area, it's usually just a matter of implementing ecologically sound management and dealing directly with some of the nastier exotic plants, if they are present. It's amazing what can come back simply with better management.
If an area has been disturbed beyond recovery (e.g. farmed), you are probably best off removing all existing vegetation and starting with bare soil. It's fairly easy to create a "prairie" by simply throwing seed on bare ground and waiting. Seed selection is a very important consideration. The best way to acquire seed is simply to hand collect it from native plants in the local area. If you can't do that, next best source would be companies that specialize in selling local ecotype seeds/plants like Prairie Moon or Ion Exchange. I wouldn't recommend planting cultivars, even of native species. They've been selected for certain traits and are often unusually aggressive, creating problems for the other species in the planting.
The hard part of prairie plantings is not getting them established, but rather maintaining them over the long term. Prairies need to be managed or they rapidly lose diversity and are often invaded by a number of invasive weeds. Areas of any size, say an acre or more, will likely need to be managed with fire at the minimum. If your site is beyond a few hundred square feet or so, and you can't burn it for whatever reason, I'd probably recommend doing something other than a prairie planting.
