The main thing is knowing what is happening under the wand and developing an eye for dirt. Experienced carpets cleaners control the speed of the wand, how much solution they're putting down, then picking up according to the condition of the carpet. You learn to know when it's a clean as it's going to get. I remember years ago, I sold an old Bobcat to another carpet cleaner. He had used mainly portables up to that point. I demonstrated it at one of his customers, which was an insurance office. I did a little bit, then passed the wand to him to try. Using the same prespray, the same flow, his area was not as clean looking as mine. He was confused but it's just the difference between knowing what you're doing and trying to copy what your're seeing. Of course it's always to have your scrubbing tools handy but proper wanding can take care of most situations with a little patience.
