Like a previous poster mentioned, we have certain ingredients on hand so I know that on any day I can throw XYZ into the crockpot and have a meal when we get home. I don't have to think about it because the ingredients are always in the pantry. I stock up on them in bulk. Like for example, canned black beans and a jar of salsa = black bean soup. Chicken + salsa = chicken fajitas. A bag of dry lentils and some water could be lentil soup. Or put dry rice, water, and a can of diced tomatoes on the stove and have a nice rice side dish for whatever meat is in the crock pot.
Also I have planned for a month in advance but I don't assign each meal to a particular day, so it could be switched up if need be.