How can I get rid of bad thoughts?

Bad thoughts can mean many things - it can be impure thoughts, negative thoughts, feelings of anger, grudge etc. And all of us struggle with bad thoughts.
Why do we have bad thoughts and where do they come from?
The Bible tells us very clearly about the source of these thoughts. "The heart is deceitful above all things and beyond cure."(Jeremiah 17:9) Jesus said that from our heart originates impure thoughts, immorality, evil ideas and so on. (Read Matthew 15:19) We are fallen human beings, and our hearts are contaminated by sin. When a person is saved by Jesus, God gives them a new heart - and that person is a new creation.(2 Cor 5:17)
But again, even for a saved person, the heart doesn't become all of a sudden free of impure thoughts. The devil will use every opportunity to tempt us and somehow make us trip. The Bible constantly reminds a believer that he/she should be watchful and continue to persevere in overcoming sins in their life.
When it comes to our thoughts, there are some practical and intentional measures the Bible recommends.
1. Cut the external supply - Be "choosy"
Our thoughts are usually a result of things that we watch, read or hear. It is important for us to check, whether there are things that we are still watching, or hearing or reading that's leading to such thoughts later on. It maybe some shows that have bad scenes, or some friends who use a lot of dirty languages, books which gives rise to wrong fantasies. As, a Christian - be very "choosy"(careful) on what your heart consumes. "but test everything; hold fast what is good. Abstain from every form of evil." (1 Thess 5:21,22)
If you find such an ongoing source - cut it!
2. Renewal of our minds
Having said about cutting bad sources, we may not be able to fully get rid off these junk stuff no matter how careful we are.(Things like inappropriate ads, what people say to us etc) Hence, while we are working on cutting off unnecessary content, we have to also work on getting more good content inside of us. A rich supply of God's word is necessary to renew our thoughts. The Word of God will help to realign our thoughts and stay on the right track.
"Do not conform to the pattern of this world, but be transformed by the renewing of your mind. Then you will be able to test and approve what God’s will is—his good, pleasing and perfect will." (Romans 12:2)
3. Meditate on these things
Many a times, we read God's word, but don't work on playing it in our minds. We should intentionally develop a habit of meditating on God's word and other helpful content.(Phil 4:8) Scripture memorization is a great thing to do, no matter how old we get. The devil (a.k.a "father of lies") will bombard our minds with his lies and we should have sufficient amount of God's word to fight his lies. Jesus overcame temptations by quoting back the scriptures.
4. Don't go easy on it!
When tempting thoughts or ideas come, immediately take a step against it. Use scriptures, pray hard, talk to God - immediately. Letting these thoughts linger around is simply giving the devil a better chance to lead us to sin.

Also, we should understand that getting tempted with bad thoughts is not a sin - but us letting it stay there or thinking for a longer period about it or not taking any measures against it on a daily basis, is. At the end of the day, we are all asked to be watchful and take heed that we may not fall.