For what the law could not do, in that it was weak through the flesh, God sending his own Son in the likeness of sinful flesh, and for sin, condemned sin in the flesh. Rom. 8:3.
Sin is never overcome apart from the faith relationship with Christ. But within that relationship with Him, there are several steps that God leads us through to overcome sin in our lives. The first is to admit that sin is sin. If you have been struggling with a problem, and have had no victory, this could be one of your difficulties. Have you come to the place of admitting that it is sin, or are you still trying to rationalize it? Has the Holy Spirit brought conviction to you on this point, or are you trying to go on what your parents said about it, or what your neighbors or pastor thinks? Victory never comes until we ourselves realize a thing is sin.
Once we have acknowledged that something is a sin, we must realize that we are helpless to do anything about it ourselves. The strong person may control his outward actions, but he hasn't overcome the sin. Sin is always from within, and is only overcome by God's power.
When we have come to the point of recognizing sin, and admitting our helplessness to battle with it, we then must realize where the battle is. In Romans 8:3 it says that what the law could no do, in that it was weak through the flesh, God sending His own Son in likeness of sinful flesh, and for sin, condemned sin in the flesh, that the righteousness of the law might be fulfilled in us who walk not after the flesh, but after the Spirit. If you are trying to overcome in your own strength, you will find nothing but weakness. But if you come to Christ, and allow His Spirit to work in you, you will overcome. If we direct all of our willpower toward seeking the faith relationship with Christ, we will have none left to fight sin and the devil. And that's how it should be, for Christ has promised to do this for us.
Another step is to recognize that God does not condemn us. God sent not His Son into the world to condemn the world. As we see the love of Jesus, and realize God's loving acceptance of us, it will break our hearts and transform our lives. And, finally, as we see what sin did to Jesus on the cross, this will become a mighty shield from temptation.