Twist the ferrule back and forth in the rag between your fingers. The bumper or hard piece of rubber at the butt end of the cue should always be maintained and in place. The bumper acts as a shock absorber to help prevent damage to the cue. Warping can be a problem, especially if you own a one-piece cue. The best way to prevent warping is to rest the cue flat on the table when not in use.
Some people store cues in a rack, which is normally attached to a wall.
At no time should a cue be leaned up against a wall, table or any other object for any length of time. This practice invites warpage and many other problems. A two piece cue should always be broken down and stored in a good case when not in use. Never leave your cue in the trunk of your car, even if stored in a case. Sun rays will heat up the trunk causing the wood to eventually dry out.