According to the U.S. Fire Administration, homeowners should clean residential dryer vents once a year at least to prevent excessive debris from building up inside the ventilation pipes which can cause risks like using large amounts of energy when operating the dryer, gas leaks and residential structural fires.
For houses using the dryer over two times per week on a regular basis, cleaning services need to be increased to reflect the extra use. There are things that homeowners can do to decrease how much debris builds up inside their dryer ventilation systems in between being cleaned.
The outside ventilation open should be kept covered using the ventilation cap. The caps have been designed to be used for this reason, and they allow the debris to get out while at the same time it prevents birds from nesting inside the vents, which prevents blockages from happening.
It is fine to periodically take the back of the dryer off and vacuum the lint out that has gotten trapped behind your dryer. However, you need to be knowledgeable about your dryer before trying to take it apart. Make sure it is unplugged and also disconnected from the gas line before you try doing this to ensure that the house and its occupants are safe.