When I came back roughly half a year ago, I guess I had the same question in mind.
I'm quite the inquisitive soul, so I set out to find out, for science, I guess. Nah jk I was lonely as fk.
So, there you go, I was back, at that time, only one contact was still alive and kicking, the one that dragged me back in the game basically with a scroll of rez. I had no guild, it was that 7 day trial for getting rezzed.
I've no guild, but he was in an RP guild, me being on an RP server.
Got along pretty well with them. I wasn't much in the way of RP, since I was mostly some crazy PvP-er, always found RP awfully slow and boring, though I love lore and stuff like that.
However that wasn't a big deal. Went in some dungeons and raids with them to help them with the RP loot, did some jolly co-operation, decided it's actually very nice to assist them whenever they asked.
I also have this policy of expecting nothing in return. Hmm though I wonder if deep inside it's all true or not. I enjoy the company, and I also get to know them better. Hmm, information is a valuable commodity I suppose... Though it comes by default, rather than expected.
Did dungeons as alts too, went in some less accessible Cata raids, did PvP togeter, in the end I'm pretty close with most guildies, I don't play right now, but we still talk. I guess doing content together helps with bonding.
Later, I sent my bank-alt DK in a raiding guild as I wanted to see MoP content.
I suppose it's the same story over there. Some ppl seemed like fun, we did some alt runs and real-ID adding, some random PvP. Hell I don't even care about rating these days, it was still hilarious.
Also, another thing I did, was while running around Shine of Moon Moon, I'd see some random ppl idling a lot. Or running around like I did. I randomly whispered them, never knew I had the balls for that, I'd die if I did that IRL. It kinda worked though it takes forever for me to think up a pretext and stop it from being awkward. 2vs2, he;s flagged, BG's! ICC25! Ended up with some on Real ID. I rarely Real ID.
So, that's how MoP was oddly social for me. With some I still talk on Skypes and stuff, since I don't play anymore.
Also, look back how you met your other WoW buddies. You need to do some things to trigger some circumstances and pull off a justification/pretext to engage in jolly co-operation.
And then you must be the cuddly pixelbundle everybody likes to be with and cuddle, not just some acquaintance. I guess friendship is what your goal is too, uh?
I really hope all this data helps! Guess we could've tried some random BG or stuff while you're here, but I don't play, not until WoD, so no point in giving ID. Also I'm EU. Though if you're same zone, and here, and looking for company, guess you active guys could PM each other some tags? Touch summoning signs, do jolly cooperation!