If you would like to keep your stamps free from ink stains, you can give the unmounted stamp blocks a coat of a water based varnish such as Jo Sonja's, which is available at craft shops or Bunnings stores. I just coat the contoured edges where you place your fingers and the base where the stamp is mounted. The water based varnish is easy to put on with a foam craft brush and dries very quickly.
If however, you are like me and have already mounted some of your stamp sets, you can still add some protection later. This tip was from my friend Christine and it works a treat. Buy some inexpensive, clear nail varnish and using the brush coat around the base of the mounted stamp and on the contoured edges. This also dries very quickly and any stains wipe off easily.
If you have got a few stains on your stamps already, don't despair. I use an emery board (that you use on your nails) to gently sand off the stain. This works well for light stains. I always keep an emery board in my craft kit to file off any 'furry' edges on card stock.