Most people were never taught about the subjunctive. I never learned what it was until I was a sophomore in college, even though I used it correctly.
"If I was" is almost always wrong, I think. The subjunctive should be used whenever you're talking about something contrary to fact. Thus, "If I were a rich man" is in the subjunctive because I'm not a rich man. However, if I said something like, "If I was there, I don't remember it," it would stay in the indicative mood because it's not necessarily contrary to fact—it's just unknown.
Does that make sense?