Regularly shake these mats (outside!) to remove excess dirt. If you don't, your mat will be spreading dirt all over your carpet, which will get ground into the fibers.

Angie's How To Maintain and Clean Your Carpets
You told us that you have carpets in your house, so now we're going to tell you how to keep them in great shape! A clean, well-maintained carpet will improve the look of any room, but a ragged, dirty carpet will make your house look like a hovel.
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If you can, vacuum your carpets 2-3 times a week, and at least once a week. This will prevent dirt from sinking into your carpet and getting stuck for good.
Nothing is worse than a permanent red wine stain in the middle of your living room.
Even if you vacuum every day, carpets are prone to smelliness. For specific odors, you can sprinkle your carpets and rugs with baking soda and then vacuum it up a few hours later. Tip: To keep things consistently fresh, squeeze some lemon or lime juice into your vacuum bag before each use. The scent will be transferred to your carpet so you can enjoy a nice citrus smell!
In general, it's a good idea to have your carpet professionally steamed or shampooed every 12-18 months. However, you may want to do this more frequently if you have pets in the house.