Do you have a screen top tank? If you do:
1) Place a humidity gauge in your tank so you know what the humidity is.
2) Try a substrate that holds moisture. All substrates dry out, but cypress seems to dry out more slowly than aspen.
3) You can place a plastic sheet over the majority of the screen top. This will help trap humidity. Make sure there is some ventilation.
4) Buy a plastic spray bottle, like the kind you might put window cleaner in, and mist the inside of the tank walls occasionally. You can mist the underside of the plastic sheet to where is forms droplets. This helps keep humidity up better than just misting the inside walls.
5) If you are using a heat light, a smaller dome will dry the tank slower than a large dome. For instance, in my 40 gallon breeder, I was using a 10" dome with a 100W black light bulb. I tried a 8.5" with the same 100W bulb. My heat stays the same, but the humidity stays 5-10 points higher. I think a larger dome spreads the heat out more than a smaller, more focused dome does.