Let go of relationships that do not serve you. That means negative people, dishonest people, people who don’t respect you, people who are overly critical and relationships that prevent you from growing. You can’t grow as a person, if you don’t have people in your life who want to grow with you.
My father had taught me to be nice first, because you can always be mean later, but once you’ve been mean to someone, they won’t believe the nice anymore. So be nice, be nice, until it’s time to stop being nice, then destroy them.