1. Wipe down the entire interior with distilled water using a clean cloth. Word of advice: do NOT use a cloth that you just washed in your laundry. You want something that has never had soap on it. A good option is those blue shop towels that are sold at hardware and auto parts stores.
2. F*ck beads. This is just my own opinion based on my own experience.
3. If the humidor has a glass dome top, get some clear silicone sealant and run a bead all around the top of the glass top *while it is closed*. Be careful not to get any sealant on the inside of the humidor.