If the stain is dry, use a cloth that is clean and soft, and rub the area with it in a gentle manner. Then, use an art gum eraser or a pencil eraser over it, rubbing gently. If neither of these techniques works, continue by rubbing the area with an emery nail file.
If the stain is oily, sprinkle it with baby powder, cornstarch or foot powder. With a soft brush, take away the powder. Repeat these steps until the powder doesn't become oily anymore. Then, restore the nap by brushing the area.
If the stain is wet, take a cloth that is clean and soft, and use it to absorb as much of the moisture as you can. After the cloth absorbs some of the moisture, make sure to turn to a clean and dry area of it, and then keep on blotting. If no more moisture is getting absorbed, leave it alone to dry completely. If the stain is no longer present afterwards, brush the suede to restore its nap. If the stain is still present, treat it as a dry stain.
There are special sprays to waterproof suede. However, remember to first test the spray on an inside seam, as this will give you some indication of whether the spray changes the appearance or texture of the material.