Most of the cleanups after a birthday party are unforeseeable. How could you have known your son's best friend was going to squirt mustard on the wall? That came way out of left field.
One thing that you can be sure of, though, is that everyone will have dirty shoes and that very few kids will have been trained to politely doff their footwear before they enter your house. If you have nice rugs, a birthday party is the time to roll them up and store them for a bit.
It's also time to pull out your grimy old rugs, carpet squares and industrial floor mats. You'll want to arrange these strategically at entrances. Kids may not take off their shoes before they come in, but they do like wiping their feet. It's sort of like marking their territory. We can't guarantee that kids won't track in dirt, but you can at least get some of it out of the way.