I responded to a post about this, and thought I would just go ahead and lay out a step by step guide for success in almost any situation.
Just so you all know, I am actaully a certified carpet cleaning tech, so the guide will be based on actual experience and textbook guidelines.
First for floor mat's
1) Go to Target or Home Depot and buy a square tub big enough for common-sized floor mat's - by tub I mean one of those storage tubs that you might put winter clothes in during summer
2) Fill the tub with a mixture of 303 Fabric and Vinyl Cleaner and warm/hot water (I use 4 oz of cleaner for every gallon of water)
Note: the reason to use this product specifically, is that is cleans without the use of detergents - you do NOT want to leave detergent residues in the carpet or it will attract new soils (the carpet will be dirty again in a few weeks)
3) After the floor mat's are completely saturated, begin aggitating the entire mat with a soft-bristle brush (if you use a hard-bristle brush you will "scratch" the fibers - fibers are made of Nylon and nylon is plastic)
4) Disregard actual "stains" for now - i.e fruit juice, ink, market, etc.
5) Remove the mats from the tub and rinse them off - you can use a hose, pressure washer, or just dump a bucket of water over each of them - this will remove all imbedded soils
6) Treat remaining stains with the appropriate stain remover
A) Artificial Dyes (Kool-Aid, etc) - use Red Relief (you will need a white towel and a clothes iron (it will leave crap on the iron so don't use your wifes iron
B) Synthetic Stains (Ink, Marker, Oil, Grease) - use Kleenrite's Volatile Dry Solvent or Kleenrite's Dissolve Semi-Solvent
C) Blood, Vomit, Food, Drinks, Pet Stains (Protein-based stains) - use an enzyme-based product (Enz-All/Pet Stain-Off/Enzyme Pre-Treatment)
All of the above chemicals can be purchased at a carpet cleaning supply company like Jon-Don
7) Rinse a second time and lay out to dry - you may want to use a wet/dry vac to remove excess moisture (water)
8) Apply a SOLVENT-based protectant such as 303 High-Tech Fabric Guard
Note: Do NOT use Scotchgard - it only protects against dirt and debris - does NOTHING for actual stains such as drinks, food, oil, grease, etc.
Done properly you should only have to clean carpet and mat's once per year!!
For actual carpet the only difference is that instead of the immersion bath process listed above, you would use the same products - just you would work from a small 2 gallon bucket and use a soft-bristle brush - you could put the mixture into a spray bottle if you want to
After cleaning you would suck excess water out of the vehicle's carpet with a wet/dry vac and then allow to air dry
Do NOT soak the carpet - use only the amount necessary to achieving cleanliness, otherwise it will take about 5 hours for the carpet to dry
Hope this helps!!!