Do you know of any tips that professional cleaning people use to clean a house efficiently and thoroughly?

I am wondering what tips and methods professional cleaning people use to clean a house efficiently and thoroughly.

I had heard that professional franchises like Merry Maids do not use water, they just use chemicals, because it’s inefficient to go back and forth to the tub or sink to wash and rinse. I think that’s gross. I am looking for something more practical.

What rooms are best to start with? How do they do the job in the least amount of time, yet do an adequate job? Do you know?