1. I've been at this for over 7 years..... so lots! haha. Started with 3 years of Japanese in college... moved onto self study when I ran out of courses. That was a really hard transition... although it got much easier after I graduated and didn't have to focus time on other coursework.
I've done textbooks, RTK, lots of JLPT prep material, used the newspaper a lot. I used to watch a lot of drama... although more for entertainment than for studying (ie, didn't look a lot of stuff up.... only if it was a word or something that came up a lot). I also used to joke that everything I knew about Japanese conversation I learned from ainori... haha....
2.
Really helpful:
Anki - holy crap, I wish I would've had access to something like this as a student. It's fast, efficient, and I can control what goes in it.
RTK - I've long stopped reviewing and have some trouble recalling some stuff when I'm writing.... but the process has by far done more for my kanji recognition than anything else I've done to learn kanji.
Talking to people - I learn more from a night out drinking with friends than I do in most textbooks.
The コラム section of the newspaper - When I was a bit more diligent student, I used to clip this out (almost) every day, paste it in a notebook and look up all the words I didn't know. Great vocabulary booster - although some of it was a bit obscure.
Not so helpful:
Sentences method - didn't work for me...
Watching or reading something for the explicit purpose of "mining" : Drives me batty. I'd much rather watch or read something for enjoyment. If there's an unknown word or grammar construction that pops up enough, I'll look it up. But otherwise I leave it be, because stopping all the time ruins the fun for me.
3. I don't think it matters what methodology you decide to follow or even so much as what learning material you prefer... if you're not willing to go out and get your hands dirty and actually try to produce and speak the language, I don't think you'll get very far.
That you can overcome SO many shortcomings in things like grammar and vocabulary by learning how to describe things... and how to understand those descriptions. I think that's one of the major reasons I can understand just about anything that's thrown at me - because if I forget a word - I describe it in Japanese. And if I don't understand something a speaker is talking about - I get them to describe it in Japanese (not always possible, depending on the situation). For me, this really unlocked the door of being able to communicate and be understood.
And QuackingShoe hit the nail on the head. Every time I read someone posting about how "X doesn't make sense" or "Explain wa and ga to me RIGHT NOW!" I just want to hand them a chill pill. If something new doesn't make sense right away - try to get a general idea of what's going on if you can and move on. Because for the most part, if you're seeing something in a textbook/hearing it in everyday conversation, you're going to hear it again... and eventually the light bulb will click on and it'll make sense. I laugh at myself when I think of a time when I struggled with things like wa vs ga; the whole ageru/morau/kureru stuff; passive voice, etc... because it's stuff that with enough exposure becomes completely second nature... and you won't even have to think about it.
4. Not bad. I'm not nearly as good about studying as I used to be... after passing JLPT 1 I've sort of gone on an extended vacation from actively trying to cram material into my brain. I still speak/use Japanese every day though... but for the moment I'm comfortable with the level I've reached and don't have a huge active desire to devote as much time to studying new material as I once did..... I need a new 資格 exam to study for, I guess
lately they're not around so much
