Revelation 12:11 And they overcame him by the blood of the Lamb and by the word of their testimony, and they did not love their lives to the death.
This is how you overcome the devil.
First and foremost, it is by the blood of Jesus.
There is life in the blood (Deut 12:23) and in the devil, there is only death.
The word of your testimony speaks the truth of the grace of God in your life.
It speaks of His forgiveness of sin and redemption from death.
The devil is defeated by the word of truth.
Finally, his defeat is sealed in the fact you have laid down your pride and life to the Lord Jesus Christ.
You are willing to die for Him, though it may never come to that.
You have laid down your life, taken up the cross, and followed Him.
Satan is defeated in your life because of what Jesus has done, is doing, and is going to do!