Have you ever asked yourself what God wants you to think about? To put it another way, have you ever asked yourself what God wants to do about your thoughts?
The answer is that God wants to fill your mind with Himself -- with thoughts and emotions that are good and pure, and reflect Him instead of the evils of this world. The Bible says, "Finally, brothers, whatever is true, whatever is noble, whatever is right, whatever is pure, whatever is lovely, whatever is admirable -- if anything is excellent or praiseworthy -- think about such things" (Philippians 4:8).
Those words were written by the Apostle Paul, a man whose mind had once been filled with hate and anger: "Meanwhile, Saul (or Paul) was still breathing out murderous threats against the Lord's disciples" (Acts 9:1). But something happened to him: He met Jesus. And Christ took away his anger and hatred, and replaced them with love and compassion and purity.
This can happen to you. First, turn to Jesus and by faith ask Him to come into your life -- and He will. Then ask Him to help you begin to see other people through His eyes -- eyes of love and compassion. Ask Him also to fill your mind with His truth, as you study the Bible and begin to fill your mind with its words. And if evil thoughts do come, turn immediately to Christ and ask Him to take them away and fill your mind with Himself.