I'll share some thoughts since I've been through a recent deconversion...
Lastly, to share my own tactics since I happen to be married to a believer... I never engage in any head-on confrontational debates anymore. I find it fruitless and that it only leads to dissent on both sides. It's difficult enough to discuss these matters... don't add resentment as a further barrier to someone listening to you and changing their mind.
I have found it helpful to simply ask questions. My wife just heard a talk on prayer and intercession and "Why god says 'no' sometimes." I found the whole thing riddled with issues, but I have come to find it more effective to simply ask inquisitive questions rather than ridicule or attack:
Things like that. After a number of those types of question (and my wife not being sure how to answer), I simply asked if she felt like the questions seemed to require somewhat convoluted answers. She said yes. Does't mean she's going to abandon belief. For now, she believes that someone "smarter than her" would be able to answer the questions... but I find it enough at the present moment for her to at least be brought to understand that the answers seem convoluted. And then I can introduce the fact that correct solutions tend to be the simplest ones that can account for all the details.
I'll depart with a flow-chart for these discussions I was just sent. It's filled with unstated assumptions and other flaws, but interesting nonetheless (LINK).
I have noticed during my dialectic adventures on the Grid that religious people, no matter how "reasonable" (i.e. moderate, unaggressive, unassuming, gentle, etc.), would get very annoyed by an assertive, dry Atheist perspective, which they tend to nickname Hollywood Atheist (interestingly, religious people tend to use this term to atheists that openly make fun of religion and are very assertive and even preachy about their disbelief, while atheists tend to use it to mean people who are atheists for shallow, weak reasons and who do a poor job of defending their stance in an argument). There is also the tendency to compare the certainty of an Atheist with that of a Fundamentalists, when they are fundamentally different in nature (pun unintended), something they do not seem to be able or willing to grasp. Not that atheism hasn't had its fair share of fundamentalists, but that's supposedly the difference between an atheist who is so out of rationalism and one that is so because they hate the Church or because Stalin (glorified be his name) told them to.
On of the things that irritate them the most is the phrase "God is Dead". A phrase that is obviously meaningless in a literal sense (although, of course, God was never a living being in the first place, by the current definition). Figuratively, it means something akin to "Our Father is dead": we are now orphans, adults, we don't need a God to tell us what to do, or what to want, or how to see the world: we decide for ourselves, we see for ourselves, we are now free... but it does feel a bit lonely, and, for those who relied on their God or Parent Figure as a crutch, it can be hard to adapt to a world without a reference, without an authority figure. A world where you are the reference, you are responsible for your own moral choices.
There are other things, specific arguments, methods of approach, that anger them and are counterproductive to the submitting of the message. Of course, the atheist message is a Brown Note of sorts to the religious mind, since it challenges their entire worldview (though in the end it all adds up to normality... except much more seamlessly). However, it would be nice to develop an approach towards theists that avoids the frontal part of their mental shields and gets into the seams, using the minimal force in the points of maximum efficiency, bypassing their knee-jerk defences...
So, here is my question to you all: how do you get your points across to a theist without pushing any of their Berserk Buttons, without coming off as a condescending and dismissive jerk, and without having to shorten all of the freaking Inferential Distance?
Developing a general algorithm would help us spread our ideals further, which, as far as I know, we think will be to the benefit of all humanity and might in fact help us avoid extinction. So, suggestions...