Muslims will be very critical of the failure of Christian secular life and immorality.
Christians should acknowledge that many Christians have not, and do not meet the high standards of Christian morals.  But Christians should remind Muslims that this is also true of Muslims.

Christians must be patient, kind, respectful when in contact with Muslims.
They must be firm in their faith in Jesus Christ and the Christian Godhead.
Christians must know their Scriptures and faith well.  
Muslims will quote the Bible, but often in a corrupted form learned from the Quran.

Christians who would dialogue with Muslims must know the rudiments of Islam and have read the Quran.
Muslims will not listen to Christians who do not know Islam and have not read the Quran.

Christians must know the development of Islam and about Muhammad's life and experiences.

Christians should be able to tell the "story" of Christianity, that is the story of God's purpose in Jesus, Jesus' life and teachings, and the meaning of his death, burial, and resurrection, and and how the Christian faith relates to this. 

The real power of the Christian faith lies in the steadfast love of God, his giving of his only son, and the love of Jesus for mankind that motivated his sacrificial death.
The atoning death of Jesus for mankind is a fundamental doctrine and foundation of Christianity.
This message is strange and alien to the faith of Islam.

Christians are taught to love their enemies, to pray for those who persecute them, and to be willing to die rather than retaliate against their enemies.
This doctrine is also alien to Islam, has been since the beginning of Islam, and continues to be so today.