We were all born knowing how to vacuum a floor, right? I mean, how hard is it? Pffft!
You turn it on, and move it around the floor. Easy! Done! Only it isn't.
Years ago, I went to pick up a vacuum cleaner that I was having repaired. Not having much disposable money in those days, getting my old vac to limp along for a few more years was essential. The repair guy and I got yakking, and he asked me if I 'really' knew how to properly vacuum a floor. "Sure!" I said, grabbing a demo model and getting with it. He smiled and gently took the machine out of my hand and showed me how to do it right.
Most people vacuum in a 'W' pattern, which is wrong. You're missing a lot of real estate that way, and you're also not 'picking up' the nap of the rug, thereby releasing the dirt. Vacuum in rows. Pick up the nap, and put it back down. And, for really dirty carpets, go over it again at a 90 degree angle.
Most people vacuum too fast, which is wrong. Slow your roll. I mean, you went to the bother of getting the machine out, so you want it to work, right? Give the machine time to do the job.
Finally, did you know that a vacuum cleaner cleans best on the backward pass? That's right. Moving it forward gets a little bit of the stuff, but a nice slow backward pass is where the real action happens.