Then I was into a few things without actually participating in the fandoms at all, but then in 2010 I got hardcore into Farscape and it has been my biggest fandom to date, measured by fandom participation.
I started by writing a lot of fanfic. That's what initially made me come to LJ and that was clearly a great decision. I started writing meta/reviews of each episode and tbh my reviews were kinda shallow and ship-focused :) but ehh it counts?? and I also started making icons. I made a crapload of them every single day and they were the most ridiculously horrible icons you can imagine but participating in farscape_20in20 made me up my game a bit.
The best fandom experience for me however was probably farscapeland, because it was a social activity where I got to know a lot of people. I participated in all kinds of fun challenges, and in these actual realtime chats which were surprisingly fun for a while until everyone started hating each other (or was it just me? I think it might have been just me :p). anyway I wish there was something similar for every fandom I like.
After that, almost all of my fandom contribution has been in the form of icons. It has been my passion for a few years now but tbh to me it's usually more about the actual graphicsmaking than about that fandom, even though I do work the best when I'm 100% into that fandom/subject.
There have been fandoms I've been into after Farscape, but online stuff hasn't really been a priority to me recently and whenever I see an interesting fannish discussion or other activity I usually don't bother participating. My fandom experiences these days are mostly just reading stuff at fandomsecrets, and browsing tumblr's ship tags (and when I'm feeling really grouchy, sometimes the anti ship tags lol).
my favorite part of being involved in a fandom is discussions with like-minded people. which there are none, usually, so this is an imaginary part. of the real fandom parts my fave thing is probably iconing, and daydreaming about my OTPs :) ♥
as for the last question - no I've never been to any cons/meetups, mostly because I'm a Finn and a student so I can't just fly to other countries whenever I want, and there are no fandom things here (for my fandoms). and even if there were cons that I could realistically attend, I doubt I would, my social anxiety would kick in plus I'm always afraid of what my online friends would think of me in person, and whether seeing how ridiculous I look would actually change how they see me as a person :D, so idk, I like to keep my online and RL personas completely separate.
sorry for the wall of text I wish there was a way to insert lj cuts into these answer thingies.