Check for leaks. If its a solid top, you can put a flashlight inside and look around the edges for light leaks. You can fix small leaks with blue painters tape. If its a glass top, you can put a dollar bill in several places around the edges, it should not pull out easily. Also, check the glass to be sure its tight and doesnt move around.
This thread will guide you through seasoning a humidor.
http://www.cigarasylum.com/vb/showthread.php?t=620