Here is one from The Hubs, we have a carpet cleaning business and he has been cleaning and restoring carpets FOREVER.
This is a wonderful tip, a friend of mine who has faithfully used this tip has told me that it has truly saved her carpet. If something spills on the carpet you obviously want to get it up IMMEDIATELY. Do not rub it, pat it dry. Now to prevent the spill from causing a stain, go get some baking soda, pour a little bit in a bowl (maybe 1/4 - 1/2 cup depending on the size of the spill) and then add a little bit of water until you end up with a paste. Take the paste and rub it into the area where the spill was and let it sit until it drys. After it has completely dried you can take a scrub brush to loosen the paste, vacuum up and be amazed that there is no stain.
He also wanted me to add that white vinegar removes coffee and pet stains!