In scripture, the Christian Bible and the Islamic Qur'an give some very similar instructions regarding debating style. Believers must continue to debate patiently, courteously, kindly and with respect whenever they see or hear their own doctrine being absent or ignored. Believers shouldn't give up on trying to convince someone, saying things like "let's leave this until later", or "I don't want to talk about it" when asked difficult questions. Also, believers should not make assertions, saying "this is so!" without providing any proper information before the exclamation marks.
The first verses we look at from the Bible says that Christians must give reasonable answers to those who ask, whereas some other verses say that preaching must be active and continuous - presumably whether or not people have asked for it.
“Always be prepared to give an answer to everyone who asks you to give the reason for the hope that you have. But do this with gentleness and respect, keeping a clear conscience, so that those who speak maliciously against your good behaviour in Christ may be ashamed of their slander.”
1 Peter 3:15-16 (NIV)
“Preach the Word; be prepared in season and out of season; correct, rebuke and encourage - with great patience and careful instruction.”
2 Timothy 4:2 (NIV)
“Let your utterance be always with graviousness, seasoned with salt, so as to know how you ought to give an answer to each one.”
Titus 3:2 is of a similar vein, saying to avoid slandering people, and to be peaceable and considerate. And 1 Timothy 3:1-11 repeats these instructions, in particular applying them as the necessary style of senior Christians and their wives (see 1 Tim 3:7 in particular - "good report of those without" means he must speak well of non-Christians) .
This isn't quite the whole story, as some verses in the Bible state that you shouldn't take the gentle, polite and respectful route. 2 John says that if you don't have the right beliefs about the relationship between Jesus-as-god and Jesus-as-man then you are godless (2 John 1:7-9), and Christians can't greet you politely nor welcome you in to church or home (2 John 1:10-11). Just to greet people with wrong beliefs, says 2 John, is to be in league with evil! This has no doubt helped encourage the intolerant and fundamentalist streams in Christian history.
The Bible (NIV). The NIV is the best translation for accuracy whilst maintaining readability. Multiple authors, a compendium of multiple previously published books. I prefer to take quotes from the NIV but where I quote the Bible en masse I must quote from the KJV because it is not copyrighted, whilst the NIV is. [Book Review]