What’s the best way to fight sin in your mind and life? Pre-emptively. LOL! You've gotten some very good responses so I'll just add some scripture.
It’s good thing that you mentioned the mind. To me, that’s where the battleground is even though the flesh plays a very large part in temptation. But if the mindset is firmly established first I really believe that Christians can be over comers more often than not.
A lot of Christians believe that dealing with sin is all about the heart. I believe that’s not enough. Some Christians believe it’s all about us on our own accord trying to ignore the flesh or trying to “punish” the flesh into submission. That’s impossible. The Bible says that the mind plays a much bigger role in this than we think.
Here’s what the Bible says about the mind in that context.
Psalm 26:2-3 …… “Test me, LORD, and try me;
examine my heart and mind.
For Your faithful love is before my eyes,
and I live by Your truth.”
Isaiah 26:3-4 …… “You (God) will keep him in perfect peace, whose mind is stayed on You: because he trusts in You. Trust in the LORD for ever: for in the LORD JEHOVAH is everlasting strength…”
Matthew 22:36-38 ….. “Master, which is the great commandment in the law? Jesus said unto him, Thou shalt love the Lord thy God with all thy heart, and with all thy soul, and with all thy mind. This is the first and great commandment.”
Acts 17:10-12 …… “And the brethren immediately sent away Paul and Silas by night unto Berea: who coming thither went into the synagogue of the Jews. These were more noble than those in Thessalonica, in that they received the word with all readiness of mind, and searched the scriptures daily, whether those things were so. Therefore many of them believed; also of honourable women which were Greeks, and of men, not a few."
Romans 7:22-25 …… “For in my inner self I joyfully agree with God’s law. But I see a different law in the parts of my body, waging war against the law of my mind and taking me prisoner to the law of sin in the parts of my body. What a wretched man I am! Who will rescue me from this dying body? I thank God through Jesus Christ our Lord! So then, with my mind I myself am a slave to the law of God, but with my flesh, to the law of sin.”
Romans 8:5-6 ….. “For they that are after the flesh do mind the things of the flesh; but they that are after the Spirit the things of the Spirit. For to be carnally minded is death; but to be spiritually minded is life and peace.”
Romans 12:1-3 ….. “I beseech you therefore, brethren, by the mercies of God, that ye present your bodies a living sacrifice, holy, acceptable unto God, which is your reasonable service. And be not conformed to this world: but be ye transformed by the renewing of your mind, that ye may prove what is that good, and acceptable, and perfect, will of God. For I say, through the grace given unto me, to every man that is among you, not to think of himself more highly than he ought to think; but to think soberly, according as God hath dealt to every man the measure of faith.”
Ephesians 4:22-24 ….. “That ye put off concerning the former conversation the old man, which is corrupt according to the deceitful lusts; And be renewed in the spirit of your mind; And that ye put on the new man, which after God is created in righteousness and true holiness.”
1 Peter 5:8 …… “Be sober-minded; be watchful. Your adversary the devil prowls around like a roaring lion, seeking someone to devour.”