Check the condition of the wiper blades. If they are cracked, or show any signs of deterioration, or if they fail to clean the glass effectively, renew the blades.
To remove a wiper blade, pull the arm away from the glass until it locks. Swivel the blade through 90º, then squeeze the locking clip, and detach the blade from the arm. When fitting the new blade, make sure that the blade locks securely into the arm, and that the blade is orientated correctly.