1. If the church wasn't true or at the least wasn't what it claimed to be, would you want to know?
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2. If the church wasn't true, how would you know?
3. If you left the church, what would you have and what would you do?
Question 1 tells you if they're capable of escaping indoctrination. Anything from a flat "no" to a declaration that "the church can't be wrong" is where you stop. If you don't, what you tell them may be immediately rejected without thought, and it will only drive the wedge deeper into your relationship without helping them out. A hasty, "yes, of course" may be a brush off, and may need to be treated as a "no". Questions 2 and 3 will tell you if it was.
Question 2 tells you if they have ever thought about this before. It tells you about their shelf. It helps you know what's important to them and what they already know. An empty shelf isn't a problem, but it does show that they haven't really thought about this before. Don't overwhelm them with information. Start on one item at a time, but go as deep as they want to go on each of those points. Look for feelings of uneasiness.
The most common objection I've experienced here is that they feel good about the religion, or they trust their feelings over facts. Follow-up by asking them what they'd say to a Catholic who said the LDS religion was wrong because the Catholic felt God told them Catholicism was the one true path? Offer examples if they don't believe you. The most common objection is a variant of the Catholic being wrong because their feelings aren't telling them to be LDS. If you get this, respond with, "how do you know you're not the one who is wronged or being tricked?" If the answer results in circular reasoning then stop. The objectivity test was failed. Save both of you from the headache. In the worse case, you could drive them further into the group  .
Question 3 is about you understanding their needs. It tells you how they will react to the fallout of information. Would you be driving them into deep depression? Would you break up their family or take parents from children? Would this information isolate them from their family and friends? Are they prepared or capable of living life in the wild, or have they fallen in love with the cage  ? If the answer is in anyway yes then you need to go slow. Help them see the joy of the world while or even before give them the information they need to free themselves.
These are based on my experience and discussions on what helped others... and what has only hurt them or pushed them back into regression. What would you add or change based on your own experiences?