PHILIPPIANS 4:8
"Fix your thoughts on what is true, and honorable, and right, and pure, and lovely, and admirable. Think about things that are excellent and worthy of praise."
Your mind can hold only one thought at at time. You control what thought is in your mind at any given time. Because these statements are true, you are responsible for what you are thinking. You can dwell on or fix your mind on what you choose. You have free will and are responsible for those choices. You determine what you think about, is it excellent and worthy of praise?
We all know someone who accepts what is false, and dishonorable, and wrong on a regular basis. We all know someone who thinks impure thoughts about ugly and undesirable things. Do you know someone who looks for the negative side of everything? They can tell you what is wrong with everyone and everything, but they have difficulty telling you how things can be right! Paul has an admonition for them and their thoughts!
Fix your thoughts on truth, not lies. Search for what is right and admirable and avoid what is false and wrong and dishonorable. Look for and think about what is lovely and praiseworthy and do not let yourself get caught up in the ugly side of man's nature. No time for pornography or things that are not reverential. Spend time with friends that are virtuous and uplifting. Keep your mind fixed on the things of God. That is WHAT WE SHOULD THINK ABOUT!