For the serious student: you can access the written lessons of the LDS church by googling the words "LDS, Preach My Gospel" and at their website you can read exactly what will be presented. For those who just need some scriptures to present... I give a general idea of the lesson points and how to respond to them below.
The Title of lesson 1 is The Restoration. Their teaching goal is to tell you the gospel of Jesus Christ has been restored through the Prophet Joseph Smith.
So the question is... was the gospel lost? Ask them to produce scriptures that say the gospel was lost. Amos 3:7 indicates that such a MAJOR EVENT would not occur without God giving a warning of it. (in the Bible) The only scriptures they can present have to do with Israel. Amos 8:11, for example, is about a famine in the land of Israel of the HEARING of the word of God (it doesn't mean the written part was lost), prior to Christ's first coming. This passage in no way relates to the NEW COVENANT Gospel.
They may switch to giving verses on the APOSTASY of the church. Their verses speak of SOME falling away, (or OT passages on Israel's apostasy) but that is not the same as all falling away. If some fall away, some are still faithful, and thus no "restoration" is needed. Their primary proof text is II Thess. 2:3, but if you study the context (verses beyond it), it refers to an apostasy or falling away that will occur when the MAN OF SIN is on the earth, who will then be destroyed by the brightness of Christ's coming. LDS instead are talking about an apostasy that occurred 1800 plus years ago. Another proof text, I Tim. 4:1 speaks of SOME turning away, not all. I asked 8 missionaries (by mail) many years ago to produce for me all scriptures on total apostasy or loss of scripture...and never got even one good verse to support the idea. INSTEAD we read that there is no lost truth in Isa. 40:8, I Peter 1:23, Psalm 100:5 and Matt. 5:18 and 24:35. THIS is what they need to see.
Another interesting thing about their total apostasy theory is that III Nephi 28 tells the story of ever-living apostles who would be bringing people to the church and to Christ until the end. This means there could not have been a total apostasy in the sense of LOST AUTHORITY. This is worth pressing home.
They may speak of lost authority, but Matt. 28:18-20 speaks of Christ having all power (authority) and His being with believers til the end of the age or world. See also Eph. 3:21
In this lesson they will say that God, when circumstances were right, reached out to the world to restore the truth. This means that He had no control over "circumstances" for 1800 plus years...until Joseph Smith was living on the earth. ?? This puts God on the level of a child who couldn't figure out to send Smith down to the earth right away, rather than 1800 years later. They will tell of the first vision, when Smith supposedly saw the Father AND the Son. When they do, the scriptures to show them are John 4:24, Col. 1:15, John 1:18 and I Tim. 1:17 Exodus 33:11, 20-23, all of which show no man can see God the Father. (See the article on First vision versions)
They will present the idea of the fullness of the gospel being brought forth, and at this point, you should go back to the idea that it is not fullness of truth if one person believes 1 plus 1 = 2, and the new truth is that 1 plus 1 = 3. In other words....their NEW or restored truth, the 3 heavens theory CONTRADICTS the Bible (Rev. 20-21) and thus we are duty-bound to reject it. (Isa. 8:20).
Quite often when the missionaries do not know how to respond to a information given (no answer) they will default to giving their testimony. I have two articles that go further into this if you need responses to the testimony:
Mormon Testimony and Why I believe the BOM