The best way is to do a reset. Just like a separation in marriage. You give each other time away to realize how important you are to one another and give a little time for the fresh wounds to heal. During that time apart, each friend should perform an honest introspection of how they could have been a better friend. When the friendship resumes, each friend must make a concerted effort to address the issues they uncovered in their introspection and try to be a better friend. It takes a conscious effort to change.