The  list  of "dos and don't's" in witnessing to Mormons  can  be quite  long, but for simplicity, there are three really  critical "do's".
1.  Control the Encounter. Even though it is your house,  if  you don't control the encounter, they will. You must be assertive  in this. You should open the discussion with your prayer, not theirs (very important you never allow them to pray over you) and  immediately go into the questions you wish to ask them. You should go through the questions step by step and then thank them, make your remarks, give a witness for Jesus, and you close in prayer.
2.  Stick  to the Subject. The minute you "pierce  their  armor," they  will try to sidestep to another issue or attempt to  change the subject by insisting on finding out about your beliefs.  Stay on track and just summarize their response to the last  questions and go on to the next.
3.  Emphasize Jesus Christ. Mention Jesus every chance you  get. Remember  that Mormons have "another" Jesus (2Cor. 11:4) and  are not  familiar  with the Bible's message of the  Gospel  of  Jesus Christ, even though they use His name all the time. Your missionary  friends  will say something like: "Good  afternoon,  we  are representatives  of  the  Church of Jesus  Christ  of  Latter-day Saints.  We would like to share a successful family program  with you and your family, without any obligation on your part and with nothing to buy. May we come in for a moment?"
Your response: (You're not going to make it easy). I already have my own religion. I'm a Lutheran
Their  response:  Wonderful. Our message is for families  of  all faiths. May we come in?
Your  response: Yes, come in for a moment. I'd like to ask you  a few questions. You are now seated with your Mormon visitors.  You have  stated that as people who wish to serve the Lord,  and  who seek  truth,  any such discussion in the spiritual  realm  should begin  with  prayer,  and you lead it! After  everyone  has  said "Amen,"  tell them that you desire to know their motives or  purposes  for  being  there, and you would like to ask  them  a  few questions. Ask them if this is agreeable to them. If not,  gently ask them to leave. If yes, then go into the first question.

[Someone  other  than myself wrote the pamphlet I'm  copying  and this is a lesson not only about witnessing to Mormon missionaries but also about pamphlets. This particular one doesn't have biblical advice. If you have let the missionaries into your house, you have  not used God's advice expressed through the second  Epistle of  John verse 1:9-11: "Whosoever transgresseth, and abideth  not in  the doctrine of Christ, hath not God. He that abideth in  the doctrine of Christ, he hath both the Father and the Son. If there come any unto you, and bring not this doctrine (the Word of God), receive him not into your house, neither bid him Godspeed? For he that biddeth him Godspeed is partaker of his evil deeds."
And secondly: to continue this interview with two Mormon missionaries  warrants two of you. The reason Mormons come in  pairs  is spiritual  power. The power is doubled when two people  in  total agreement confront one person who is not in agreement. Doing this sort of interview alone puts you at their mercy and in jeopardy.

20 Questions
Question  1. I know that you are missionaries, but what  is  your purpose or your end desire for this visit?
Response:   (It  will be in the nature of a statement  that  they would like you to learn about their church or "way of life.")
Question 2. Is the Mormon Church a Christian Church?
Response:  Well, of course it is. We bear you our testimony  that it is.
Question 3. I'm a Lutheran. Is my church a Christian church?
Response: There is truth in all faiths.
Question  4. That's not what I really asked you. Does the  Mormon church believe that the Lutheran church is a Christian church  in exactly  the  same manner and sense that it believes  the  Mormon church is a Christian church?
Response:  Not  really, you see, we have some  additional  truths that we would like to share with you. (Don't settle for  anything less than a no!)
Your response: Simply put, you mean. NO!
Question  5.  In fact, isn't it true that  your  church  actually teaches that my church's creed is "an abomination in the sight of God." and it's professors (members) are all doctrinally  corrupt? Do you believe this to be fully true?
Response:  (The Mormon must answer these yes. It will be hard  to extract from them, but stay with it until you get a flat  unsoftened YES in each case).
Question 6. Is Jesus Christ Your Savior?
Response: Yes, of course!
Question 7. Exactly what did Jesus Christ save you from?
Response: From physical death. He died to atone for Adam's transgression.
Question  8.  Do you mean He atoned (personally  paid)  for  your sins? (1 Peter 2:24, Galatians 1:4)
Response: Not exactly.
Question 9. Exactly, how are your personal sins atoned for?
Response:  (Will pertain to works and judgment of  each  person's works)
Question  10.  In other words, you are saying  you  believe  that Christ's  death  paid  for Adam's sin only  and  the  immortality promised in the scriptures only means that we will be resurrected to be judged for our works?
Response: Yes. (Don't settle for anything less!)
Question 11. Do you believe the Bible to be the Word of God?
Response: Insofar as it is translated correctly.
Question  12.  You believe then, that the Bible is  basically  in error? What percent? Where? What books? Chapters?
Response: (They will avoid giving specific answers. Don't  worry, you will never get one here.)
Question  13. When you appear before the final judgment,  do  you hope to become a God, just like our Heavenly Father is a God?  Is that your goal?
Response: Yes
Question  14.  Will your works have to include  being  a  Mormon, being married in the temple, being a member of the Mormon Priesthood, doing your genealogy? Serving a mission? Attending all your meetings?
Response:  Yes  (The Mormon will be reluctant to talk  about  the temple, so let him avoid it. The temple ceremonies are secret and held very sacred. Oaths are made that could put their very  eternal lives at stake to talk about them.)
Question  15.  Did our God have to go through such a  process  to become a God?
Response Yes (Don't settle for less!)
Question 16. Does He (our God) have a God over Him?
Does that God have a God over Him, then?
Response: yes, yes.
Question  17.  Then if you do everything right, you  will  get  a chance to become a God just like our God. Is that true?
Response: Yes
Question 18. What about Goddesses. Do you believe that God has  a God-wife, our "Heavenly Mother?" In fact, more than one wife?
Response: Yes (To both questions!)
Question  19. Does this God of ours have a physical body? Did  he pass  through mortality before becoming a God? Just like you  are hopeful of doing?
Response: Yes.
Question  20. Are these teachings those which have been given  in the "restored" teachings taught by your prophet Joseph Smith?
Response: Yes.
Summary:  Let's  stop now and see if I'm correct  in  summarizing what you have said.:
1.  All  "Christian" Churches except Mormons are  in  error,  all abominations before God.
2.  The Bible is at best, a weak source of truth. It is in  error and it's teachings about salvation are in error.
3. We must each earn our own salvation.
4. We can become Gods.
5.  God  was once a man but progressed into Godhood. So  did  our Heavenly Mother.
6. All is known because God sent a prophet in these latter days.

You must show your Mormon friends [correction, they are not  your friends]  that these concepts are totally outside the  Scriptural concept  of Christianity. In fact they are signs of a cult..  not even a sect. (Refer back to the section, "Is the Mormon Church  a Christian Church?") Your goal here is to actually peel back  both sheep-skin  layers. Tell them you are not trying to debate  their doctrine, but to establish IDENTITY.
First, they have shown you that they really are not the sheep  of your  Christian flock. They are at your house to pull you out  of your  flock  and into the one they call home. Get them  to  admit that they are. In fact, being deceitful in encouraging others  to consider them as "in the same flock."
Next,  use the results of the questions to show that they  really are  not  a  Christian sect. Go through the tenets of  a  cult  . Please  remember. DON'T DEBATE THE POINTS, Just get them  to  see that  there is a difference and that difference truly makes  them not Christian but a Christian sounding cult. Do not allow them to draw you into an argument.
The  Lord  will quicken their hearts to accept this  truth.  Your work is only to lay the information before them. The Holy  Spirit will put it into their hearts...