Normally, brooms are not thought of as requiring cleaning. However, a clean well-maintained broom will not only last longer than one that is not looked after, but it will do a better job when sweeping.
One key to extending the life of your broom is to store it with the head of the broom off the floor or ground, (which means it either gets hung on the wall or from the ceiling) or stand it up on its handle. This will help prevent a buildup of dirt or moisture on the broom head. Also, the broom will not deform which (when this happens) restricts the brooms ability to sweep efficiently. If your broom is dirty or moldy from moisture, try hosing off the broom head, then scrub lightly to remove debris or mold. If there is lots of debris in the broom head, try combing it out with an old wide-toothed comb or with your fingers.