The best carpet shampoo advice you will ever hear is to know which products you are going to be using before you apply them to your carpet; you should also know exactly why you want to go do a good shampooing as it can be unrealistic to try and extract certain stains with a cleaner that is not meant for the job. Dirty carpets can be a pain to try and lift out old, set stains but it can be done if you arm yourself with the proper knowledge!
Carpet shampoo machines are going to be your best bet when it comes down to the cleaning of your rug or carpet. It is good to avoid dry foam carpet shampoo because it can set in your carpet and not properly dry leaving you with a sticky and unpleasant rug. The way that is best to clean is to get your hands on a machine that uses warm or hot water that will mix with some kind of cleaning solution to maximize the effect. Take special care to make sure you are using a cleaning agent that is designed to work with water, if you use a dry foam product you can turn your carpet into a bubble bath.
If you are using a machine, carpet shampooing is as easy as pie, the only hard part is going to be changing the hot or warm water to recycle it and keep it fresh. There are companies who will clean your rugs for you, but you should empower yourself and go out and get a good carpet shampoo rental machine and do it yourself to save a lot of time and money. If you think the process is to complicated you should reconsider that notion as it is relatively simple.
Carpet shampoo cleaners work by using special chemical agents to lift the set dirt and grim out of your carpet, in conjunction with the hot water they act to simultaneously lift the dirt out of the carpet while chemically treating it. Understandably there are people who do not wish to use harsh chemicals on their rugs, if you find yourself aligning with this thought then you should be aware that there are a number of organic and “green” shampoos out there as well as homemade solutions you can make yourself that involve vinegar.