sandman said...
not storing it wet in a hot place (ie car) which will sweat off all your bladder valves which will then give way as your pumping up for the downwinder of your life.
Good advice Sandman, just adding that this can happen regardless of wether the kite is wet or not.
Once had 3 (very dry) kites in my car during the day. The result: a total of 7 valves came off two of the kites

Just for the record, the one kite that was unaffected was an old airush (lift 15.5)