In order to reduce the rate of random encounters, you first need to find Cyrus and add him to your party. From the menu, go to Skills and then learn two additional skills with Cyrus (a total of 4 is needed). This will then allow you to "Equip Support Skills" with him. Select Evasive Maneuvers as your support skill which reduces the rate of random encounters. It only works if he is in the party.