One of my favorite scriptures, which I have incorporated into my daily prayers is Psalm 19:14 (KJV): "Let the words of my mouth and the meditation of my heart be acceptable in thy sight, O Lord, my strength, and my redeemer."
The reason I've adopted this as my daily prayer is that while I don't always do it (Just ask my kids!), controlling my mouth is at least possible. Controlling my thoughts ("meditation of my heart") is harder. I can keep a stray, offensive thought from jumping right out of my mouth to the detriment of all innocent bystanders, but keeping it from even being a thought can sometimes be quite a challenge! Since my thoughts impact and determine my behavior and my attitude, I have to pray for help with that every single day.
Much has been written about the power of our thoughts. Bookstores are full of books that promote the power of positive thinking. Hericlitus, a philosopher and author (who lived approximately from 535-475 BC), had this to say: "The soul is dyed the color of its thoughts. Think only on those things that are in line with your principles and can bear the light of day. The content of your character is your choice. Day by day, what you do is who you become."
Perhaps the last verse of that childhood song should warn, "Oh be careful little mind what you think!"