We should be most militant with ourselves first, never giving in to prideful or otherwise sinful thoughts, much less words or actions.
The North American Martyrs were trained from childhood, as all children in faithful Catholic families have been, to discipline themselves with mortification, prayer, and good works. Then as young men they studied for the priesthood, were trained, and then were hand-picked to teach the Faith to the savages in the New World. They were more civilized than we might ever hope to be, as far as I can understand, because their whole culture nurtured the Catholic Faith. I will never know what it might have been like to have been trained from such an early age not only by my parents, but by each and every one of my family members, neighbors and teachers. Of course there were sinful people in those times too, but because the Church was free, it was more difficult to sin then than it is now.
When these French Jesuits came to the New World they were confronted with real savages, as we all know. I think I recall reading from the Jesuit Relations that almost every sentence that came from the mouth of any of them, including children, contained either a curse, a lie, something vulgar or some blasphemy. I can't imagine surviving even 5 minutes in that kind of situation without falling into sin myself, but I didn't have their training.
They're our examples. They were prepared to die before they would consent to a single venial sin. We know what the venial sins are against pride and anger and other species of sin. I think we must form the habit of avoiding sin before, during, and after we think of converting anyone else. Others might disagree, saying 'But if a house is on fire, you don't think of anything but saving those who might be trapped inside, and if they refuse to be helped, you knock them out and drag them to safety.' I would answer that's not a good analogy because there are no true forced conversions.
I'm pretty sure that every possible means of getting to Arius was tried before that shot was delivered by St. Nicolas. I think I read that Arius was given a long time to voice his views before that shot. St. Nicolas did many charitable works, as you probably know, before and after that shot. How many of us can say we've trained ourselves to that degree?
Since we don't live in a Catholic culture, we have to humble ourselves and start with appropriate goals suited to our state of soul. Too much ambition in this practice can be prideful, and too little can be slothful. Either can lead to despair.
I think the most challenging duty we have is this one to try to convert others. But once we've acquired the habit of overcoming our self-love, it should be easy to talk to non-Catholics about the Faith.