Dig out the area for the patio or sidewalk with a shovel and compact the soil with a vibrating plate compactor. Soft soil areas benefit from tightly packing the soil to get rid of air pockets; air pockets lead to settling. Compressing the soil tightly provides a stable base for the concrete to lie.
Dig 6 inches below the frost line with a post-hole digger. Tamp the base of the hole with a 2-by-4 piece of lumber. Add 4 inches of a sand and gravel mixture to the bottom of the hole and tamp the gravel to compact it tightly. Mix concrete with water in a wheelbarrow or trough. Pour the concrete into the hole until concrete fills the hole. Allow the concrete to set for 72 hours before continuing with the sidewalk or patio installation. Dig and fill holes with concrete every 18 to 24 inches throughout the sidewalk or patio field beginning 4 to 6 inches from the edge of the patio or sidewalk.
Add 4 inches of a gravel and sand mixture to the base of the compacted sidewalk excavation or 6 inches of a gravel and sand mixture to the base of a large patio to provide adequate drainage under the concrete structure. Water flowing under a concrete patio or sidewalk causes erosion that leads to a sinking sidewalk or patio. Run the vibrating plate compactor over the sand and gravel mix to compact the ground further under the concrete. Avoid compacting over the concrete support piers.