Start by soaking for an hour in a solution that is 1 part white vinegar and 3 parts water. Rinse the garment well and allow to dry. The vinegar will kill mold, and also helps to stop colour bleeding. To deal with the staining, Mix some oxy clean (or similar) and warm water in a jar or tupperware container with a lid. Drop the garment in, shake vigourously several times. Allow to sit in solution for an hour. Rinse very thoroughly, allow to air dry. At this point there should be a vast difference. Feel free to repeat any steps as needed. I also use a stain remover product at times if the stains are bad. That sits on the garment for 10 minutes before the oxy solution.
Hope this helps...
Jon