You start with Jesus. Because they believe in Jesus. We have that in common. Protestants need to acknowledge that.
If you start by trying to show them all the errors of Catholic practice you're likely to just hit a wall of resistance.
Don't forget people were raised from early childhood with all these things. The Holy Spirit convicts when the time is right
Which is often why evangelism is best done in close relationships like the disciple settings. You build trust with the individual and show them you actually care for what they think and wont go all heretic on them lol. A offensive response automatically makes people defensive. In a defensive mode it is as if we shut down from listening and straight to defending our worldview.
Explanation from psychology
"We all naturally strive to reduce uncomfortable thoughts and emotions that sit poorly with our dearly held beliefs. Such is the way when we deny evidence of an unfaithful partner or of the abysmal performance of a beloved sporting team. Our beliefs become impervious to the facts in a process psychologists call
cognitive immunization.
Cognitive immunization helps to explain why some beliefs become even stronger when challenged. They also help to explain how we cannot let go of some beliefs in the face of overwhelming contradictory evidence.
Immune beliefs are almost impossible to challenge with reasoning and structured argument. Try the following experiment: Google "greatest ever superhero" or something similar, and glance through the stunningly vigorous mass of blog, forum, and web article debate. Our mental firewalls defend immune beliefs well, so it really doesn’t matter if Superman should logically be able to defeat Batman to the keyboard warrior already committed to the opposing position.
Classic psychology studies show that we have trouble remembering the times when our personal beliefs have failed the test of outside evidence. This is because our minds automatically neutralize clashing information—such as that awkward moment when practitioners of a doomsday cult realize that the world did not come to an end when predicted. They just need to reset the date to accommodate a variable that went uncalculated in the initial forecast. . .
In fact, one characteristic of strong and resilient beliefs is their internal logic and structure, even when they defy logical verification as a whole. As a result, believers come to arguments well-prepared, having become adept at using their
confirmation bias—the natural inclination to avoid any information that contradicts a strongly held belief, while seeking out information that strengthens it. "
Roughsoul1991 now speaking. So the trick is not to make them feel attacked.