Use a big tractor, 3 furrow 12" bottom plow and plow it deep if there are no rocks or roots. Disc it in both directions, Sideways and lengthways.
Then you have a choice of Spring Tooth or Harrow to further break it up. If you have a roller, now is the time. If you are planting grass on it, wait a few weeks and spray with RoundUp to kill new green stuff. Wait a couple more weeks then plant grass seed. Plant it twice as heavy as recommended. Some scatter straw or mulch over it, to help retain moisture and thwart birds as it germinates. Water it twice as often as you think it needs.
Good Luck.