If your looking for a good do it yourself stain remover this video does a good job of explaining how to remove a carpet stain, with some minor exceptions. First, I'm only going to focus on the carpet stain remover and not the production quality of the video. As a professional carpet cleaner in Tampa FL I love watching videos of people showing how to clean spots in their carpet. Some of the things people do to remove carpet stains shock me, but most are relatively similar.
Starting out with a good base for your solution is important. Every carpet cleaning solution on the market is made up of at least 60% water. That's right starting off with good old H2O is the best way to start. If your stain is a water based then a mixture of water and vinegar is a great cleaning solution. I suggest a 1:1 ratio. If the stain still doesn't come out try adding some heat to the equation. You can use hot water or microwave your DIY stain remover for about 30 seconds. This will increase the cleaning power of your solution by 10 fold.
If you have an oil based stain then you can start with the same carpet stain remover and add about 10 drops of dish soap (I prefer Dawn, because it really is tough on grease). Be Careful not to use too much soap or your stain will be likely to return.
Make sure after you blot up the carpet stain to rinse it with some plain water to get out and residual cleaner. I also recommend putting a clean dry towel over the spot and standing on it for about 1 minute to get up any extra moisture.