The most important thing about spot removal is never scrub the spot! Always blot the area with a light colored cloth or plain white paper towel. Aggressive scrubbing with a brush or towel will almost always set the stain and distort the carpet face yarns.
Unfortunately, carpet spotters that appear to work miracles on television will not perform nearly as well in your home. It is impossible to completely remove large spills of any substance other than water by simply applying a cleaning agent and blotting. Some residue will undoubtedly remain in the pile, and the spot will probably reappear in a few days. Deep spills need to be extracted from the carpet fibers. Small spills can generally be removed by the homeowner.
Most spots you find on your carpeting are going to be either water based or oil based spots. Water based spots are caused mostly from dropped food or spilled beverages. Oil based spots are usually the result of tar or oil being tracked in on the soles of shoes.
Another type of stubborn spot is a tannin stain which is commonly caused by spilled coffee or tea. Red wine stains are common and can be very difficult to remove. Pets account for a lot of spots on carpeting as well. Sometimes they have accidents, and the resulting spots can be difficult to remove. Spots caused from vomit can also be stubborn, especially if any substance containing food dyes were ingested. If these types of spots haven't been set by previous attempts to remove them, we can almost always remove them completely!
Many liquid medications and beverages such as Kool-aid contain strong acid dyes and cannot be removed by using standard spotting procedures. Spills of this nature are best blotted to remove the bulk of the substance, then left alone until a professional can remove them. Attempting to scrub these stains with normal spotting solutions can permanently set the stain and distort the carpet's pile.
Some ink is water soluble and can be removed using common spotting procedures. Ball point pen ink is not water soluble and should be removed by a professional.
Latex paint is extremely hard to remove if it is allowed to dry. Paint penetrates the carpet's pile quickly and needs to be flushed out quickly. This job is best left to a cleaning professional.
Candle wax can usually be removed by using the heat transfer process. Apply several layers of white paper towels over the wax and heat the wax with an iron. Change the paper towels often, and do not get the carpet fibers too warm or they will melt! The pigment found in colored candles will permanently stain the carpet even though the wax is easily removed.
Most water based spots can be removed by following this procedure: