There is one happening that you must understand. Soils rise when full of water and fall when dry. its a molecular thing. This will cause your home to rise and fall. Thats why cracks will go away in the fall and winter and spring, but come back in the summer.
I would, as I religously do, place a soaker hose all around your home, 16 inches from the foundation and during the summer times and time of drought, I will water one half of the foundation all night and the other the next night. I will do this every 10 days or so. It does work, but it has to start in the spring and go until the fall rains.
If your soils begins to seperate from the foundation and you can see it readily, then you are late. Its like re hydration, you need to drink before you get thirsty.