Before spending lots of money on seeds you need to first analyze your soil. It can be a scientific test, like one sent to a lab or one that you can get from home depot for 5 bux. The other is a bit better, however I have done each one and have found my own basic knowledge would have been enough. So first you need to know about the organic material in it. This means food for microbes, worms, etc etc. The darker it is usually means the better it is. The soil on most of my land was like chert, very red, and only weeds grew there, and sparsely. So I needed to build top soil. First I did lots of legume/nitorgen fixers, like clover, and peas (year one). Once I had some nitrogen in the soil I started to plant bio mass builders like sunhemp, and vetches. I also started to add lots of wood chips to the soil.
Now if you have livestock like I do (kunekune pigs) you can skip the legumes part by doing what I had done as an experiment. Densely stock the field you want to work on. Feed the animals, and let them deposit top soil, then rotate them as necessary. This will give you LOTS of nutrients.
Next you need to work on your armor and biomass. The sun hemps and vetchs do this really well. Or you can also just add wood chips to the surface of your soil. This protects the soil from nutrient loss and water loss. Once you have these 2 items you can start to successfully plant other grasses to add diversity. Here is a list of some i have tried. These will vary depending on your area.
Herbs (garlic, rosemary, cilantro)