The beginning for me was when my Bible study asked me about Judicial Committees and what they were for. I showed him James 5:13-15, which was the standard scripture we used to explain the role of the JD (at least that I was aware of). My Bible Study simply said "but that's talking about healing someone from literal sickness". I knew he was correct and then I started finding other similarly twisted scriptural interpretations.
After that it was a long process of looking at various bible translations, the interlinear etc about homosexuality and so on, then the JW Facts site - earthquake stats was a biggie for me, because I remembered having to tell people on the doors that there had been more earthquakes since 1914 than in all the time before that....