This video shows you how to clean stains out of just about anything. The video contains two sections on carpet cleaning tips. I really like the part about getting candle wax out of a carpet. I use a similar technique to get candle wax out of carpet but I'm a professional carpet cleaner by trade so that's cheating.
If using an iron on your carpet to remove wax makes you nervous swap out the iron for a steamer instead. You can use a fabric steamer or even a steam mop. A steamer will get hot enough to melt the wax without damaging the carpet. When using steam to melt the wax make sure to use a towel instead of a paper bag so the steam can pass through and contact the wax.
The other carpet cleaning tip is not something I would use on my carpet. There is way to much soap in that mixture and you the spot that you clean out will just start to darken again as people tread over the spot. I will pick up soil and you will be caught in a vicious circle of using a dirt-attracting solution to remove dirt.
I clean carpets in Tampa FL and I recommend using carbonated water and about 5 to 7 drops of dish soap to remove stubborn spots in the carpet. I have mixed that quick little spot remover several times and it works great on most spots, except pet urine which is a completely different article.