In my opinion I sort of disagree with the comment above as I cant get my humidity in my exo terra terrarium to get a higher average than 39%. But my last 3 sheds have been perfect.
First sign of going into shed I put a good amount of spagnum moss all around the viv and have to spray it 3 or 4 times a day or it dries out because I use a heat lamp. Spagnum moss is a god send and iv never had a problem with it. I also put a little bit in the corner of both hides but make sure it's damp and not wet.
I also put a second water bowl under the heat lamp which does help quite a bit. I use bark chips as substrate which has been the best for me for humidity by far !!
This all gets my humidity between 55 and 80 % so the average is quite good and has worked great for the last 3 sheds.
I would like to mention that I have a lucky reptile fogger which is pretty useless with a heat lamp as it goes from 30 to 70 and then back to 30 in about 1 minute. I don't like using it much because of the risk of RIs tho.
I don't have this setup anymore as iv switched to a rack to expand my collection and would like to add that my BP seems so much happier in a rub than she ever did in the exo terra