First, what most people think of when they think of 'atheists' is 'someone with no morals and no values'. There's many reasons for that, and most of them stem from an historical willingness to conflate people who lack belief in the Christian deity - or any deity for that matter - with people who are anti-theist; Which is to say, people who actively deny the existence of the Christian deity, and seek to destroy the organisation of Christianity.
No matter if you merely lack belief in the Christian deity, lack belief in any&all deities, or are opposed to organised religion, or are opposed to Christianity in particular, Christians will label you 'atheist' meaning 'someone with no morals and no values'. It is therefore important that at the beginning of the debate, to define what 'atheist' exactly means. It is important in /any/ debate to use clearly defined terms in order that the debate does not get bogged down in Semantics later on. It is also may be important to define what a 'Christian' is, too - to handle those folks who like to throw out the No True Scotsman fallacy.
I've found that the best definition is simply to limit 'atheist' to 'someone who lacks belief in any and all deities, nothing more, nothing less.' This makes it clear that morals, ethics, virtue, duty, citizenship, etcetera etcetera - even up to /actually practicing a religion/ are all entirely out of the question here - It's entirely a matter of belief in /the existence of deities/. This also weeds out the people who are merely there to monger hate and slander you by conflating atheism with any negative strawman they want to build.
Now, as a (rather extreme but illustrative) example - I am an atheist Zen Buddhist. I practice Zen Buddhism as a religion, and I totally lack faith and/or belief in deities - the Buddha/buddhas aren't deities to me. They're not deities to many Buddhists, either, but have degenerated into a popular conception of 'deities' for many Buddhists and in popular Chinese, Tibetan, and Thai belief.
The notion that someone could both lack belief in deities and practice a religion really tends to blow many Christians out of the water. They just cannot handle the fact of my existence, and are unprepared for it - some just claim that I have a false religion and idolatrise the Buddha, and/or spout anti-buddhist hate/lies. One fellow on one mailing list was so sore that I kept tearing up his weak Christian apologetics, that he proceeded to froth at the mouth with anti-buddhist lies immediately upon learning that I am Buddhist - and continues to froth at me from my Trash bin. "I have only ever prayed one prayer, and it was thus - "Oh Lord, make mine enemies ridiculous." And it was granted." -- Voltaire.
Also, because a lack of belief is not actually a positive position - it is simply a state of being - there are no doctrines to defend, no conspiracy, no 'agenda'. I also make the distinction - which any sufficiently educated Christian will make - between /faith/, which is held despite facts - and /knowledge/.
Almost every Christian has faith in the existence of their deity. They may conflate this with knowledge of the existence of their deity, and indeed most of the 'debate' comes from the Christian apologetics attempting to produce /knowledge/ that "/proves/" their /faith/, and the critique (our critique) of that knowledge. None of them actually produce /proof of the existence of their deity/.
Atheists, by contrast, have neither knowledge of the existence of a deity (please, produce some that's other than speculation or debate over the particulars of a purely human phenomenon, and be the most famous person in history!), nor do we have faith. This is directly analogous to the Christian having no knowledge of, nor faith in, the existence of leprechauns. Convincing us to convert requires that the other side either inspire faith (which is an historically untravelled path), or produce verifiable knowledge (which is the vast majority of Christian apologetics/arguments, all of which are debunked time and again.)
Some atheists will move into the territory of anti-theism, and begin to critique the history of Christianity. I feel this is a bad choice - it then becomes a history debate, and history is determined by the victor... oftentimes, the 'victor' being the same church that burned the Library of Alexandria and forty cartloads of Judaic codexes, slew millions, etcetera... Still, bad idea, because it lends merit to the inherent argument that all theists make - that of the existence of their deity, which they presume - and often beg the question of the existence of.
For my own part, I know little about the details of Christian Apologetics. I feel it is irrelevant to argue about who did what to whom and why, when the question of what they are quibbling over - the (will of and thus existence of the) Deity - is undecided and may in fact be undecidable.
The first axiom of the Christian's argument is that their deity exists.
There is no apparent proof of this, it this premise is un-necessary to explain anything we are aware of at the time, and indeed most of the arguments that attempt to address the existence of 'deities' in general, fail. No-one can even agree on what constitutes a 'deity', nor how to authenticate that a given entity is a deity. Most of Christian apologetics is, however, the attempt of the Christian to either ignore this or to somehow persuade the listener of the existence of their deity by preponderance of a mass of incoherent, inchoate and often debunked 'facts' regarding the phenomenae of their religious movement.
The most relevant analogy of this to apply to Christians is the fact that everything Jesus did, can be reproduced by magicians, scientists, medical doctors or even surpassed. David Blaine, Penn & Teller, Randi, all can make example after example of this.
I mentioned briefly that atheists are merely people who lack belief in deities, nothing less, nothing more. I wish to stress this - if you decide to recognise this, you will spend all your time destroying the strawmen of 'atheism' that Christians put forward.
This will eventually lead to the argument of the ultimate source of morals, and which morals are best, and the assertion by theists/Christians that 'relativistic morals' - morals derived from good faith in humanity, experience, rationality, reason (from Buddhism even) - are somehow inferior to 'absolute morals' - morals as 'handed down by a divine entity'. I haven't done enough to construct a comparison of these, nor enough on building/proving the merits of a rational morality. To be honest, better and more dedicated professionals than I have spent entire careers without making much of any progress in it. I feel it is extremely important, however, and cannot stress it enough - defeating the popular notion that atheists lack morals, ethics, moral guidance, goodness, etcetera is my number one goal and I feel should be everyone's top goal.
Recent opinion polls have stated that atheists are the least trusted and most hated group / minority in America - because everyone equates 'atheism' with 'moral-less, ethics-less, sociopath', etcetera.
I hate to repeat and deny the awful accusations that Christians have always slandered us with, but I wish to also make it clear and present to every atheist that /this is how we are perceived/ and that it needs to change. I also want to open discussion on how to do this.
Excelling in our chosen professions, arguments, debates, work and personal lives isn't enough. We should overcome society's pervading prejudice against us by marginalising it to the wackos like Fred Phelps and the KKK.