First off, make sure you are planting things that are beneficial to each other in patches. Check out my post from the other day and it has a link to a good companion planting guide. Next make sure to rotate your crops every year. A good combo to plant to build the soil is the 3 sisters. Corn, pole beans to climb the corn and squash for ground cover. The beans feed the corn nitrogen and the squash keeps the weeds out.

In my garden I use newspaper to completely cover the ground. Cut holes for the plants, wet it down and cover with straw. Your garden looks to be about the same size as mine. It took me a little over 20 bails to cover it but it makes for a great compost mix. Hope this helps.