What works for me with the humidity is:when the snake starts getting cloudy eyes before shedding. I dump half a cup of water into the aspen bedding right above the under tank heating. It keeps the humidity high just during shedding. In a week when the snake is done shedding the humidity goes back to normal.
If you have a glass aquarium its hard keeping the humidity up. You can cover the top of the aquarium with plastic about 85% more or less as needed to cut off all the airflow. If you dont want to cover the tank just add a little water aboave the under tank heater right in the substrate. This system works great with aspen or cypress bedding. I would reccomend aspen though.