From my own personal experiences in doing Catholic Apologetics, I submit to you my rules for conducting effective apologetics:
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Rule #1: Most debates come down to the question of authority so know about the Magesterium. **
Be prepared to discuss and defend the authority of the Magesterium of the Catholic Church. Most debates eventually come down to the question of who has the authority to officially interpret and define matters pertaining to faith and morals.
For example, sometimes in a debate I will give a person a scriptural reference backing up a Catholic doctrine. If the person says, “That’s not what that Bible passage means”, I challenge them to explain with what authority they claim that their personal interpretation of Scripture is the universally correct one, and that all interpretations contrary to it are wrong. As you know, Catholics believe the Magesterium has the God-given authority to officially interpret and define Sacred Scripture and Sacred Tradition. But Protestants do not believe that anyone on earth actually has this authority. And yet many will go ahead and act like they do themselves, by emphatically telling people what is and what is not the correct meaning of Scripture.
Rule #2: Sola Scriptura will come up A LOT! So be prepared.
Know how to properly refute Sola Scriptura (i.e., “Scripture Alone”), and do not get tricked into playing by the Sola Scriptura rules. For example, take a look at these posts and you will see people attempting to get Catholics to defend Catholic doctrine within the restrictions of Sola Scriptura:
forums.catholic-questions.org/showpost.php?p=7229103&postcount=45
forums.catholic-questions.org/showpost.php?p=7292227&postcount=93
forums.catholic-questions.org/showpost.php?p=7291200&postcount=73
Here is a long but informative thread where I and many others tackled Sola Scriptura in several different ways:
forums.catholic-questions.org/showthread.php?t=515287
Rule #3 Always double-check the other person’s references.
Whenever someone debating against Catholicism starts quoting the Catechism, the Early Church Fathers or a saint, never assume that they are faithfully representing what these sources say. I always double-check, and many times I see that such sources were deliberately quoted out of context. Also check the index to see what all the sources say about the topic at hand. Many of the works that get cited in apologetic debates can be read online, so you don’t necessarily have to have a massive library in your house in order to do this.
A good example of this sort of thing can be seen in this post:
forums.catholic-questions.org/showpost.php?p=7760347&postcount=9
Rule #4 Catholicism = Truth. Respond accordingly.
When defending aspects of God with non-Christians (including atheists), insist on defending a faithful representation of what Catholicism actually teaches. For example, lots of people use the term “omnipotence” but people may have different understandings of what that term actually means.
Here is a recent example of an atheist trying to drag me away from discussing God according to Catholic beliefs to instead use a more philosophically “acceptable” definition of God. You’ll see that I saw the trap and resisted the ploy:
forums.catholic-questions.org/showpost.php?p=7770910&postcount=98
Rule #5 My Cardinal Rule.
I call this my “cardinal rule” because it is the thing I have stated the most in apologetical debates. “No Catholic teaching contradicts the Bible, Catholic teachings only contradict certain people’s personal interpretations of the Bible.”
When I started doing apologetics, the Catholic Answers “Faith Tracts” were extremely helpful. They give quick, clear and concise answers to most of the questions and challenges that come up in debates:
catholic.com/library/faith_tracts.asp