Many of them can be thrown in the washer. Check for a tag.
How big is it? You can put it in the washer if small enough and it can stand washing in the machine. Otherwise, put it over a railing or fence, and use your hose to get it wet. Then scrub it with a brush and soapy water, then rinse clean and let it dry.
If you can fit them into the washing machine I would wash them on a gentle cycle and line dry. If not you can take them outside and was them with a pressure washer.
My Nan used to out the rugs over the washing line and beat them to get the dust out. I guess if it doesn't fit in the washing machine you could use upholstery cleaner.