Do you have a screen top? If so, maybe cover it 2/3 of the way. Maybe even cover part of it with a damp cloth. How big is your water bowl, you could buy a bigger one. I know one poster said he has a hide with damp sphagnum moss in it.
I'm not experienced at all (not even a snake owner yet), so I'm just saying these things as general common-sense suggestions. Somebody correct me if any of them are glaringly wrong.
Just out of curiosity, where do you live? I live in Maryland, and I don't anticipate having too many problems with humidity because the ambient humidity here is usually pretty high as it is. I just plan on doing a couple of the things listed.