As often as necessary. We need to form our habits for our habits form us. To repent often and whole heartedly turns us into people who are habitually open to the transformative grace of God’s mercy. Scott Hahn has a good book on confession. In there he says confession is like medicine. You keep going to the Doctor and getting the pill you need for your blood pressure, or ointment you need for that nagging rash. In the same way, we go to the sacrament of reconciliation as often as we have “missed the mark,” which is the literal translation of the Greek word for “sin” (harmatia) in the New Testament.
If you haven’t been to confession in some time here’s a video that details some of the steps to confession.