Velcro is a marvellous invention that makes fastening things easier. It works by having two strips, one of them made of tiny, scratchy hooks which latches onto the second strip, which is softer and looped. However, if strings or other fine debris gets tangled in the hooks, the hook side can lose its effectiveness. Likewise, the finer, looped side can get dirty, making it harder for the hooks to maintain their hold. When this happens, the Velcro just needs cleaning to restore it to its former usefulness.
Separate the two strips of Velcro by pulling them apart.
Run a pick, a metal comb or special Velcro cleaning tool through the hooked (the scratchy side) of the Velcro. Remove any strings or other debris wrapped up and trapped in the hooks.
Use the sticky side of duct tape to clean the softer, loop side of the Velcro. Simply press the tape onto the Velcro to lift out any dirt clogging the loops which may be interfering with the hooks' ability to cling.
Wash the Velcro with soap and water if it is exceptionally dirty. Be sure to get all the soap out and to dry it thoroughly.
Press the Velcro strips back together. They should be as good as new.