My favorite stain remover is a bar of Ivory soap. Wet the stain then rub some Ivory into the stain and scrub a bit. Leave the soap on the stain until you wash it. It doesn't hurt to be left in for a while and may even work more of the stain out. Most of the time the stain will come out with the first washing. Occassionally, it takes another treatment. This has worked for me for many years. I like it especially for any grease/oil stains on cotton that don't seem to respond to any other spot treatment.
Be sure you use a bar of Ivory soap not dish detergent.