It depends on what kind of caging you are using. If you are using a glass tank with a screen top, you're gonna have to worka little harder to raise your humidity. If you are using a rubbermaid or customized cage, it won't be hard at all. Some easy ways to raise humidity are:
-using a larger water dish.
-Misting the cage.
-adding a humid hide to the cage.
-using cypress mulch as a substrate (this stuff hols humidity like none other).
You could cover the screen lid with contac paper if you are using an aquarium - do it on the inside so it keeps them from rubbing their noses on it to boot.
also placing sphagnum around the cage helps to raise humidity - when you change the water each day mist the tank and mist the moss, it will hold the humidity better.... don't use this as a substrate but you can put a pile or two so that you snake can either wrap them up or climb right in when he/she needs humidity.
I covered most of the screen lid, except for a small rectangle where the heat lamp is. In the space next to the heat lamp, I folded a damp washcloth and placed it in that space. It hasn't dried out, and it gave me another 10% humidity.