When Paul says to put to death the deeds of the body “by the Spirit” (Romans 8:13), I take him to mean that we should use the one weapon in the Spirit’s armor that is used to kill. Namely, the sword. Which is the word of God (Ephesians 6:17).
So when the body is about to be led into a sinful action by some fear or craving, we are to take the sword of the Spirit and kill that fear and that craving. In my experience that means mainly severing the root of sin’s promise by the power of a superior promise.
So, for example, when I begin to crave some illicit sexual pleasure, the sword-swing that has often severed the root of this promised pleasure is: “Blessed are the pure in heart, for they shall see God” (Matthew 5:8). I recall the pleasures I have tasted of seeing God more clearly from an undefiled conscience; and I recall the brevity and superficiality and oppressive aftertaste of sin’s pleasures, and with that, God has killed the conquering power of sin.