We fight evil first by fighting against the ugly and low tendencies in our heart, which - over time if we let it develop so in us - can become 'our first instinct'.

We have to - using the grace God offers us in the Sacraments, prayer, etc - go against and reorient these tendencies, which through sin, indifference, swallowing the silliness of secular culture have clouded our intellect and dulled our will to do the good & see the truth.

From Fr Francis Fernandez (at the end quoting Saint Augustine):
"...The slightest faults of others are exaggerated by our personal pride, whereas our own perhaps much greater defects are minimised and explained away. Moreover, pride tends to see in others what are really our own imperfections and errors. Hence Saint Augustine gives this wise piece of advice: Strive to acquire the virtues you think your brothers lack, and then you will no longer see their defects, because you yourselves will not have them(St Augustine, Commentary on Psalm 30, 2, 7)