What is the best way to convert a Christian to Islam?
I'd first prove to them that trinity is a man-made lie. See Answering Trinity section where every single so-called
"trinitarian verse" in the Bible is refuted.
Then, I'd prove to them that the Bible is corrupted
and altered by the Church and men.
Then, I'd show them what parts of the Bible do Muslims believe are closest to the Truth, and why?
Then, I'd prove to them that Muhammad and the Religion of Islam were foretold in the Bible.
Then, I'd concentrate on the Oneness of GOD Almighty and stress it out real good to them,
because it is the only mean for Salvation -- is to believe in GOD Almighty as the One True Living Undivided GOD and King.
I'd then show them the place and status of Jesus, Jews, Christians and non-Muslims in Islam.
Last, if they start sharing their personal stories about how GOD Almighty saved them from danger or trouble, and how the Holy Spirit was there for them and inspired them, then I would tell them that Allah Almighty can still love them and have the Holy Spirit guide them and save them from trouble, because He does it all the time even to non-Muslims and non-Christians too, because He is the Most Merciful. See also The Holy Spirit in Islam.
Allah, Islam, Quran, Muhammad questions and answers.
What is the place of Jews, Christians and non-Muslims in Islam.
Contradictions and proofs of Historical Corruptions in the Bible.
Why did Allah Almighty allow for the Bible to get corrupted?