Some things I learnt from Joyce Meyer's "Battlefield of the Mind" and Watchman Nee's "Release of the Spirit".

Ms. Meyer starts of her book with a verse from Proverbs which I find really moving, both spiritually and philosophically.
For as he thinks in his heart, so is he. (Proverbs 23:7)

Another verse from Romans puts it in more detail.
Those who live according to the sinful nature have their minds set on what that nature desires; but those who live in accordance with the Spirit have their minds set on what the Spirit desires. (Romans 8:5)

If anyone struggles with their thoughts like I do, you'll understand how much this verse stood out for me. So often in our Christian walk, we are led by what we think is right. Or what we think is God's plan for us. Suffice to say, its our thoughts guiding our actions. But Romans 8:5 says those who live according to the Spirit will have their minds set on what the Spirit desires.

So our actions affect our mentality?
Yes! Our mind has been "trained" by our actions since we were born. When we received salvation, our spirit was awakened, reborn, stirred up, re-kindled etc. (You get the point) But our physical and mental facilities remained the same. Therein lies the problem of ALL Christians.

Do not conform any longer 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)
I think many are familiar with this verse. I once believed that when paul said "do not conform" he meant that we were to rebel against the world. But I learnt that I was wrong. The opposite of conformity is not rebellion. When we rebel, we are still doing things in the flesh and by doing things in the flesh, we might be successful for awhile, but it will drain us. We're still doing battle on the world's playing field. I missed out the key point of the verse. You can almost hear Paul's plea. Be transformed! Be transformed by the power of the Spirit of God as He gives revelation. Be transformed by being in fellowship with God. Be transformed by being empowered and taking authority back from the devil. So that we claim back our dominion over things that are rightfully ours.

Our battlefield may take place in the mind but this is spiritual warfare. I remember in when was going through SISPEC in army, everytime we were getting ready to charge at the imaginary enemy, I would hold my rifle tight and mutter to myself, "Locked and Loaded!!" And it occured to me that its the same in the spiritual realm. We have to be locked in the Word of God and loaded with prayer and praise. Prayer is one of the best weapons.

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 (2 Corinthians 10:4-5)

Bringing every thought into obedience. The weapons lay at your feet. The question is, would you take up arms and fight?