1. Always dry the skis with a towel or such, and then let them stand apart fom each other to dry thoroughly before strapping them together or storing in a ski bag.
2. Try to avoid placing wet skis base to base and/or in a ski bag before you have thoroughly dried them (see 1, above). If you must transport them wet in a bag or base to base to get them home from skiing, immediately remove them from the bag and begin Step 1., and turn the bag inside out or open it up to let it dry thoroughly before using it again. Superficial rusting will start very quickly if you transport wet skis together.