Cold water: Dip the garment in cold water for a day. This will help to tighten the fibers. Take it out and use it after drying.
Steam: Steam is not a good option for pressing pants, but if you are dealing with cotton pants, a small amount of steam will do. Keep the steam press over the mark and release the steam. This is a good technique for lighter spots.
Vinegar: Add some vinegar with your detergent. Vinegar acts as a bleaching agent.
Hydrogen Peroxide: Dip a piece of cloth in the hydrogen peroxide. Put it over the mark and press gently. This can reduce spots and shine.