plant seedlings 
plant seeds directly into the soil 
broadcast seeds over the surface

You can try a combination of methods to see what works best for your site.

When starting a prairie garden, planting seedlings may prove to be the most effective use of time and resources. You can get seedlings from your local nursery or reputable regional plant sources. 

Seedlings For beginner gardeners, seedlings are easier to plant and grow since seedlings have a higher rate of growing and succeeding throughout the growing season. Seedlings should be planted once the soil has warmed in the spring. Broadcasting seeds Planting can also be done by broadcasting seeds over the area. A few people can do this by tossing seeds to the ground while walking across the site. Several other people can walk over the site pressing the seeds into the soil. You'll have to use more seeds to make up for the ones that birds will eat.

Direct planting of seeds
Planting seeds directly into the soil can be more time consuming, but often these seeds have a better success rate. Some seeds, even if they are planted directly into the soil, may not grow the first season because air and soil temperatures and moisture content may not be suitable for sprouting. These seeds may grow the following year.