I heard many times from Rabbi Chaim Shmuelevitz, the late Head of Mir Yeshiva in Jerusalem. "The commandment to refrain from speaking negatively against others does not start with what we say when we speak. Rather, it starts with what we think about when we think about another person."
The Torah obligation starts with our thoughts. When you master the ability to see what is good about other people, their virtues and positive attributes, their strengths and accomplishments, then you will speak positively about them. Knowing that they have many positive qualities and have done much good, you will find it easier to refrain from violating the Torah prohibition against negative speech.
(Growth Through Tehillim: Exploring Psalms for Life Transforming Thoughts, p. 86)