The most essential is nitrogen. A soil test will help determine your garden's needs. Typically, part of the needed fertilizer will be worked into the soil before planting and additional side-dressings may be added during the growing season. See Earthworm Corner. Plants generally prefer a pH between 6.5 and 7.8.
Alkaline soils tend to lock up nutrients.
Acidic soils can release elements at toxic levels. Soils in our area tend to run on the alkaline side. Again, you may want to consider a soil test. Local nurseries usually stock local favorites. From time to time this website will feature a local favorite.