Forums, plain and simple.
Read them, answer threads, ask questions. Having the forum community to act as a teacher and you also teaching people who come here is a great way to learn your content. Much better than trying to go it alone and figure it all out yourself, though definitely do your own research and establish your own opinions and understanding, occasionally the people here can be wrong.
I can easily say that the majority of my knowledge was gained from the community at large, and that I know many others who have learnt from what I have contributed here. Its very much give and take.