The "active zone" for soil movement is about eighteen inches deep, so keeping the top area of soil around the house damp and well watered during the hot summer months can really help minimize shallow foundation movement.
Plumbing leaks under the slab or around the sides of the house can be the biggest cause of foundation problems as the soil swells and pushes against the house foundation, causing movement. Watch for any changes in power or water bills and follow up to check for unseen or unknown leaks of cold or hot water.
The bearing soil, or the soil under where the house is built needs to be properly packed to avoid movement from the weight of the house. Sometimes softer areas will give way and cave in, causing the slab or foundation to actually crack. This is a serious problem that will continue to get worse over time.
