A little more info about your current setup will help us better. For instance, are you using an aquarium with screen lid or wooden viv with sliding glass front or some other type of enclosure? Are you using a heat lamp or UTH or some other heating element? What sort of substrate are you using? What are your current humidity levels at? Are you curious because it is an "all the time" issue, or only because of an impending shed?
Assuming you are using a glass aquarium with screen lid, as most people are, you can cover the top of the screen with a towel, leaving only a couple inches on one end open. This will help to keep humidity in there.
You can use a larger water bowl/dish on the warm side of the cage, which should help it to evaporate and create humidity.
You could use dampened sphagnum moss as part of your substrate or in a humid hide.
There are several things you can do to increase humidity in your enclosure. The ansers to some of the above questions will help narrow down the solutions you need.