Turn the garment inside out and run it under cold water, taking care to prevent the stain from bleeding further into the surrounding fabric.
Rub a few drops of liquid laundry detergent into the stain. Rinse well with cold water.
Mix together 1/4 cup white vinegar and 1/4 cup water. Dip a rag or washcloth into the solution and blot the stain several times. Rinse well with cold water.
Apply a laundry stain remover to the stain according to package instructions. Rinse well with cold water.
Wash the garment as usual. Check that the stain is gone, then lay the garment out to dry or run it through a low-heat dryer cycle. If the stain is not gone, repeat the first four steps before drying the garment, as heat will set the stain.