You've already got some great advice, but just to add a couple ideas. You could get a larger water dish and put it on the warm side, that will help bump up the humidity. Make sure that if the top of the tank is open-a mesh lid, that you cover it with a towel or plastic wrap. Just make sure that if you are use a heat lamp that you don't start a fire. Heat lamps are going to lower the humidity no matter what.