You discover a box of your favorite cigars that you left in a closet for six months, and the cigars are as dry as a bone. What do you do?
First, have patience. Put the cigars in a humidor that hasn't been charged in the previous week. Let them rest in the slightly dry humidor for a few days so the cigars absorb some humidity. Then, partially fill the humidification system, letting the cigars rest for another week before fully charging the humidity regulator. This process will ensure a slow absorption of moisture, preventing the cigars from getting too much humidity too soon. If you shock the cigars from too much moisture, they may burst.
If you have a cabinet-style humidor, first place the cigars as far from the humidification device as possible, moving them closer to the humidification device little by little over a period of six weeks.
In any case, do not light up until the cigars are supple to the touch. A dry cigar will burn too hotly, and the flavor will seem burned or carbonized.
The same principle applies to cold cigars or ones that have been stored frozen, a method some people use. (There's nothing wrong with this method except that the cigars don't age.) You must allow the cigars to return to normal temperature slowly. If you light them too soon, the abrupt change in temperature may cause them to crack open or explode. Give chilled cigars at least two or three days at the proper temperature in a humidified environment before lighting them up.
Adopted from Cigar Aficionado.