For follow-up discussion and general commentary on the topic. Comments are sorted chronologically.
Well, what if that person is a kid, about 13? Is there any way just to plant the seed for trusting Jesus and not works? And to put a different point of view on the other things Mormons believe that are, by Christian belief, incorrect?
I talked with a couple Mormon boys and an older Mormon man for several hours once. I had about 8 pages of notes on the Book of Mormon (contradictions with scripture, historical questions, some points on other Mormon books, etc.) - as well as about 100 post-its in the Book of Mormon they had given me to read. The younger boys were highly interested, but the older man kept trying to take over the conversation whenever he thought he was losing control. One thing I talked a lot about was the Melchizadek priesthood from Hebrews (we are all priests of Christ, not a select few).
The young boys were not firm in their beliefs, but the interesting thing is that the older man was not firm in the belief itself, either. For him, it was a position of power. He wanted people to follow Mormonism as the 'only church with the authority to lay on hands and give spiritual gifts' - but he did not disbelieve that others had spiritual gifts or that Christians weren't saved. It seemed as if Mormonism was just a means to an end for him, so that he personally could have a position of authority. It also seemed that he knew that the religion was false.
I would guess it would vary by person and age, but don't be afraid of saying something wrong and be open to the Spirit leading you about what to say. Observe reactions, as that can also help show points where they have doubts.
Yeah, thanks! That's really good advice. This person is really nice and is naturally happy. She'd be a wonderful Christian. She loves the Mormon church and is very attached to it, but she has the same perspective I have about her church: I respectfully will listen to you, but I won't go to your religion.