or if you can't ditch the lights right away I've heard that if you put the water dish halfway under the light or so it increases the humidity, makes sense but probably only slightly increase. Yeah put some sort of plastic over part of the lid. What kind of substrate? The Product rating section tells what substrates best hold humidity. Basically switch to undertank if possible, a larger water dish might help a little, check your substrate, and cover part of your lid (don't suffocate your snake!)