also substrate helps. in our tanks that are filled with mulch (florimulch aka cypress mulch) we see 60 -70% humidity, where the tanks with astroturf reads 40-50% humidity. I've adjusted the humidity in the tanks with astroturf by adding a second water dish that's really shallow and porus and stuck it on the warm side, brings the humidity up to 60-70%.
another thing you can do is take an air pump used for an aquarium and have it pump air into the water dish, this makes the tank some what more humid. or if you've got the space, build a waterfall.