Martin Lloyd Jones in his book Spiritual Depression made this statement I found helpful as I think about training my mind to meditate on truth and speak truth to my heart :
Have you realized that most of your unhappiness in life is due to the fact that you are listening to yourself instead of talking to yourself? Take those thoughts that come to you the moment you wake up in the morning. You have not originated them, but they start talking to you, they bring back the problems of yesterday, etc. Somebody is talking. Who is talking? Your self is talking to you. Now this man’s treatment was this: instead of allowing this self to talk to him, he starts talking to himself. “Why are thou cast down, O my soul?” he asks. His soul has been depressing him, crushing him. So he starts up and says: “Self, listen for a moment, I will speak to you…”
The main art in the matter of spiritual living is to know how to handle yourself. You have to take yourself in hand, you have to address yourself, preach to yourself, question yourself. You must say to your soul: “Why are you discouraged”—what business have you to be disquieted? You must turn on yourself, upbraid yourself, condemn yourself, exhort yourself, and say to yourself: “Hope thou in God”—instead of muttering in this depressed, unhappy way. And then you must go on to remind yourself of God, who God is, and what God is and what God has done, and what God has pledged Himself to do. Then having done that, end on this great note: defy yourself, and defy other people, and defy the devil and the whole world AND his lies.