As some have said, Old School is different things to different people. It's less about the material or the ruleset than the DM, IMO, that makes an experience reminiscent of my early days of gaming.
I learn more every day but since I began in pre-Internet days, I guess I mostly learned through trial and error and from a couple of friends who also took turns behind the screen. Picked up a few extra tips while at Gencon in the 70s and 80s.