I have done this several times using this method:
First, try lightly sanding off a corner or two and some bits around the edges. Perfectly crisp edges are a dead give away.
Next soak the label in strongly brewed tea (hot or cold) until the label takes on the amount of staining you wish.
When the label is damp but not wet, take some instant coffee, crumble it in your fingers above the label. This will easily produce the foxing as mentioned above. After it dries, iron the label flat and sprinkle a few drops of oil on it to add authenticity. Several subtle effects achieve a much better finished product. No need to stink up the house!
