I have been making a serious effort to focus my mind and thoughts on Jesus Christ and good Biblical topics.
One of the BEST passages is this well-known one:
"Finally, brethren, whatever things are true, whatever things are noble, whatever things are just, whatever things are pure, whatever things are lovely, whatever things are of good report, if there is any virtue and if there is anything praiseworthy—meditate on these things."--Phil 4:8
AND............there has been a giant "side-effect" which is:
When I redirect a negative, accusitory thought and turn my mind to anything noble, just, pure, lovely, good report and of virtue then the very NEXT thing that happens in my mind is that I praise God.
Because it seems like all the pure & noble and praiseworthy things to focus on are also the very things that God has given.
I wind up praising pretty much non-stop due to the wonderful content and quality of thoughts.
It is a GREAT side-effect.
There are a few more verses in case you are new to the concept of cleaning your brain and thoughts. Here are a few:
taking every thought captive----
"For the weapons of our warfare are not carnal but mighty in God for pulling down strongholds, casting down arguments and every high thing that exalts itself against the knowledge of God, bringing every thought into captivity to the obedience of Christ..." II Cor 10:4-6
the mind of Christ----
"Let this mind be in you which was also in Christ Jesus..." Phil 2:5
in this one we learn that the Word of God is able to discern the thoughts of the heart:
"For the word of God is living and powerful, and sharper than any two-edged sword, piercing even to the division of soul and spirit, and of joints and marrow, and is a discerner of the thoughts and intents of the heart. 13 And there is no creature hidden from His sight, but all things are naked and open to the eyes of Him to whom we must give account."---Heb 4:11-13
AND my favorite, set your mind on things above----
"If then you were raised with Christ, seek those things which are above, where Christ is, sitting at the right hand of God. Set your mind on things above, not on things on the earth. For you died, and your life is hidden with Christ in God." Col 3:1-3