Thoughts about thoughts

I have become fascinated with thoughts.  Every moment of every day, even as we sleep our minds are producing thoughts.  Something is always going on up there.  And as the scriptures attest, "As a man thinketh, so is he", so shouldn't we be a little more interested in what we think about?  Day dreaming can be fun and inventive, but to let our lives be constantly involved with just random idle thoughts can't be very motivating or uplifting, can it?  How often have you heard someone begin an apology or explanation with the words, "I just thought"?  I believe that we can be and even must be in charge of what we think about and I believe that what we choose to think about while we are conscious effects what our minds do while we sleep.  Ever spend a restless night after having an argument with someone or watching a scary movie that replays in all your dreams?  Another example, have you ever spent a day trying to work out a solution to a problem, gone to sleep and during that sleep had the solution come to you?  Perhaps your mind was working away on your waking thoughts and was able to solve the problem. 
  So if thoughts are so important, I want to be in control of what I think about.  I will not surrender my mind to outside interests, be that friends, movies, internet, or other evil interests.