Being comfortable with your Faith starts with knowing your Faith. You should know your Faith enough to share it with others and that confidence will speak for itself and stand on its own.
CA has two excellent books that I recently purchased that will assist you in dealing with Latter Day Saints and those from the Watch Tower Society:
When Mormons Call: Answering Mormon Missionaries at Your Door by Isaiah Bennett, “a former Catholic priest who converted to Mormonism and then returned to the Catholic faith. He spent two years as an active Mormon, even serving as a teacher in the Mormon Institutes of Religion, and knows the religion from the inside”.
Answering Jehovah’s Witnesses by Jason Evert which “walks you through the doctrines of the JWs, revealing where and why they’re wrong–giving special attention to favorite verses and standard topics that a JW will use in rejecting the Catholic faith”.
One of the most important things I took away from these books, especially the “Answering …” book is to treat them with respect and kindness. The Watch Tower Society prides themselves on being rebuffed, even hated, because that is what Christ said would happen in the Gospel of St. Matthew (10:22).
Also, ALWAYS take their literature and, if you have time, keep them on your doorstep for as long as possible. Make idle chit-chat if you are unprepared to discuss Doctrine. That way, you just might prevent another soul from losing their salvation when you delay them from speaking to others and giving out their publications.
I have two WTS members that come by every month when they have the new “The Watchtower” and “AWAKE!” magazines. Cliff and Reggie seem to be good men, just woefully misinformed and I have already corrected them on several Catholic “myths” they tried to pass off as true. I still haven’t told them, directly, that I’m Catholic and I just ask them questions about the WTS that cause them to stutter and stammer and then try to change the subject. Most of their poor salesmanship revolves around putting down other religions but can never seem to be able to present a cogent argument why I should renounce Christianity for the WTS.