You want to have everything ready for the arrival of the concrete. All site prep involves excavating of some sort. Footings need a trench, while slabs need to have enough soil removed for the sand or gravel base plus and concrete that will be below ground level. To prevent the soil from settling under the concrete, it must be poured on undisturbed soil. In warmer areas with firm soil, where freezing is not a problem, the concrete can be poured directly on the prepared soil unless the building code calls for a sand or gravel base.
Forms When pouring footings, setting up forms can be as easy as making sure the soil is stable.
If it is, you can use the trench itself for a form. Otherwise you will need to build forms to keep the concrete where you want it. To support a wall, continuous footings need to be 6 to 12 inches thick. The forms are built from either 2x6 or 2x12 lumber. The forms for 6 inch footings are supported by stakes about every 3 feet, while 12 inch footings are staked every 2 feet.