If you don’t properly store your skis during the off-season you will ruin your skis for next season.
During long periods of warm summer temperatures your skis will oxidize -dry out- leaving them slow, slow and slow. You cannot fix oxidized bases. If you forget to store your skis properly you'll probably need to buy new skis next season. $$$
So what to do?
You need to clean the bases of your skis and store them WAXED.
Step 1: Clean the bases with a fancy ski tuning scrub brush, scotch-brite pad, clean towel or even paper towel. There are best/better options, but generally everything works good-enough. You don’t really need water or soap but it can’t hurt. You just need to get the dust and dirt off the bases.
Step 2: Wax the skis with a ski-specific glide wax (like Swix, Toko, Dakine). For this purpose, general all-temperature universal wax is fine. Put on a thick coat and make sure you cover the edges. Once again, there are best/better ways of doing this step but generally slapping on a good coat of decent glide wax is sufficient. Ski tuning irons work better than household irons but it is not important. Cheap irons are fine.
Step 3: Turn the din settings on your bindings down to their lowest value.
Step 4: Store skis in a dry place. I live in Utah, so everywhere is dry. If you live in a humid place, consider storing your skis in the basement.
Step 1: Make sure the liners are dry.
Step 2: Clean the boots with a little soap, water and toothbrush.
Step 3: Much more important than Step 2 is to buckle your boots before storing in a cool, dry place. Warmth and humidity degrades plastics.