OOh I like Ian's format, so I will copy it!
Step 1 As an 11yr old, I read the bible on my own and thought much of it wasn't fair or didn't make sense. Had it explained to me with Witness reasoning which I couldn't refute and even if I could I would have just gotten a beating for it!
Step 2 Studying the All Scripture Inspired Book, in my 20's, I thought some of the reasoning on how we know the Bible is true was very circular. I didn't know what circular reasoning was, I just thought it was weak logic. But I waited on Jehovah for clarification. None was forthcoming for 15 years.
Step 3 Went to university, studied some biology, learned some critical thinking skills, how to weigh credible source material, etc. Now, I had a hundred more questions that weren't even in the reasoning book or the watchtower and I was afraid to ask anyone but my husband. I knew the society had no answers in their literature. I thought the questions had never even been asked before.
Step 4 Did some personal research on the internet, and found AJWRB. Found out many witnesss had asked the same questions as me and many more I hadn't even thought of. And, they had credible sources of information to back them up! Found a bunch more sites and a bunch more questions.
Step 5 Lived with cognitive dissonace for a few years while I tried to figure out how I could reconcile my disbelief in society with some nice people, good freinds and good moral way of life (for some)
Step 6 Became very ill, too ill too go out in service and attend meetings. While away from constant programming/brainwashing, realized I didn't miss it at all and nobody appeared to be missing me much either and I had no desire to go back because I didn't believe a word of it anymore. My only service consisted of studying with my son, who has never had fear of questioning any authority. Refusing to lie to and use guilt and fear as a teaching method, I subtly encouraged his disbelief and tried to deprogram him because I was going to be shunned by my own kid over my dead body! Yes, I counted time for apostate witnessing! I love the irony of that!
Step 7 Once I admitted I had no reason to believe the society had any special knowledge from God, all those old questions came back and belief in the Bible fell about a week later and doubt about God a week after that. So I was agnostic for a few months. This was due just to my own logic/reasoning but nothing to really back it up.
Step 8 Read every essay, thread and debate about atheism on this site, I could find. Non-belief became firmer and firmer. One essay in particular demonstrating no real difference between atheism and agnosticsm was the final push that made it OK for me to say I was an atheist. It doesn't mean I am saying God can't exist. Just that I don't believe he does because I see no evidence. I don't have to be able to prove it. It's OK to say I don't know exactly how we all got here. None of us do!
There you go. How to become an atheist in 8 easy steps or your money back!