For me it was in university, where on my first Sunday I went where the groups heading to churches were congregating and followed the first group I came across. In the providence of God, that group went to a presbyterian church with good Bible teaching (although I didn't know it was a presbyterian church and I didn't know what Presbyterianism was at that time). It was through the teaching I received there, and seeing it was consistent with the Bible that I came to be convinced, although it took a while before I stated such. I particularly like the way the Canons of Dort present the doctrines of grace.