Moving air picks up water vapor. Place plants on a tray of wet pebbles. The water evaporates upward from the surface of the stones, creating a more humid micro-climate around the plants. The pots MUST sit above the water line. Placing a small saucer beneath each plant will insure this.
Group plants together so they can benefit from moisture that evaporates from each-other.
Put especially sensitive plants in terrariums, where you can control the environment more easily. For more information, contact your local University of Minnesota Extension Office.