What made the spot? Depending on what it is, it's treated differently. Lipstick would be one thing, red wine another.
Its like wine
Mix one part Dawn dishwashing liquid (the plain old blue kind, in the big bottle that usually sits on your sink), with two parts hydrogen peroxide
Read More http://www.glamour.com/fashion/blogs/slaves-to-fashion/2008/10/style-secret-the-only-spot-rem.html#ixzz1yB1ZQ6O4
It is not advisable to put soap on the carpet as it is difficult to extract it & the residue it leaves attracts dirt & the spot reappears. The best product for wine is Spot Shot. Kroger & Publix grocery stores sell it. Home Depot & Lowes should have it as well.
I agree with Lee Anne - do not use soap. I've used Spic N Span.
My go to product is Krud Kutter. I has taken dried finger polish, paint, wheel chair grease, and last night sweet and sour sauce out of my carpets over the years. But do test first. I have never had it discolor anything but you can't be too safe.
@Twck2 I get it at Fred Meyer. Most hardware/paint stores carry it, Amazon has it and most of the big box stores should have it too.
A dinner party saw an entire glass of red wine fall to my lightly colored carpet. Tried everything on the list to remove red wine. Peroxide finally took it out completely. And since it turns to water after air exposure there's no residue whatsoever. You may want to test for colorfastness first.
I brought a bissell streamer that took it out