First thing is get a good soil test for pH and N,P,K. That is the key for sure. No sense in pouring money into seed if the soil is in the right condition to support it. Nitrogen, phosphorous, and potassium will respond pretty quick with fertilizer. Lime will take a year or two to really take effect. Your local Ag extension service or farm store can lead you in the right direction.
I love putting food plots in and have experimented with a lot over the years. Having won some and lost some, I basically plant two basic mixes now in addition to the farm crops we use for hay for our cattle:
1. Half of the plots I put in a warm season annual mix of milo, haybeans, and jointvetch. I have a couple shady valleys that only jointvetch works well in. Its an early season magnet.
2. The other half I plant is a cool season annual mix in the fall: Oats, winter peas, a brassica (turnips or canola/rape), and crimson/arrowleaf clover. I mix it up myself, but its also common to find a similar mix at your local feed store in the fall. I like the arrowleaf clover in addition to the crimson. (it extends the growing/grazing season). Plus its just more fun to figure it out and try different things each year.
I'm by no means an expert. Honestly I just like to do the plantings and see it all come together. All of this I've gleaned from a variety of sources. The best I've found is from the University of Tennessee. They have a big foodplot publication in PDF format available free. Its a big document,
try this link for 40 pages of great information. PM me if you want more info or if the link won't work for you.