Philippians 4:8 (ESV)
whatever is true,
Whatever is honorable,
whatever is just,
whatever is pure,
whatever is lovely,
whatever is commendable,
IF there is any excellence,
If here is anything worthy of praise,
THANK ABOUT THESE THING
This appears to be a very specific list of God's ideas about our thoughts. I've been hearing some about something called "Cognitive Therapy" speaking about changing your negative thoughts to positive ones.
As I've pondered this personally, I have felt that though yes, I have negative thoughts on my own, once I go to that place they become much worse, and get increasingly negative as I dwell there. I believe there is an aspect where my initial thoughts can change into a bombardment of thoughts from the great enemy Satan. It is no longer just me. For me this verse has become increasingly relevant. I can change the thoughts, yes. It has to be a deliberate choice. But it's not just positive thoughts in the place of negative thoughts but Godly thoughts, those that bring HIM into the arena. Thoughts that need to start with praise of the LORD and reaffirming who He is and then reforming those thoughts after His kinds of thoughts.
i.e. I am feeling like nobody loves me LORD. Thank you that you love me. Open my understanding to see the people and events in my life in a true light. If there are those that don't love me, LORD guide me to a Godly love toward them. Where in truth they do love me, let me see that truth.
I know this is a bit simplistic, and there are deep issues in our minds and thoughts we have to capture and change but it seems to me our first stop in change is to begin with Praise to our LORD. And seeking understanding and change found in His promised wisdom and insight.