It's going to be hard to follow Tim on this one, because over the last year he's pretty much been the poster boy for how to get things done on AudioJungle :).
In fact, maybe I should start this with some tips on what not to do. I have not yet spent much time on self promotion (any viewers of my profile page will notice that it's woefully slim compared to other top authors). I opened a Twitter and Facebook account but keep forgetting I have them - I think I've tweeted something like 5 times. I don't own a television and don't listen to the radio or popular music. People keep talking about Dubstep and I have no idea what that is :).
Here's are the few things I have done over the past 1.5 years I've been on AJ:
I recently joined up with SoundCloud and posted a few AJ songs, and it seems to have boosted my sales a bit but that's all completely anecdotal. That boost also coincided with the newer search stuff AJ did a couple of months ago, so I'm not sure what has had more of an effect.
I do post on the forums every now and then, and I agree with Tim that it's not going to be the key to getting sales, but I do think it gives some decent exposure, especially to new authors.
I completely agree that collaborating with VideoHive authors is huge. I've had a couple authors contact me to use my background music, and have definitely seen sales of those songs go up as a result.
I guess what's worked for me the most is that the type of music I'm composing and posting is sort of a simplified version of what I do well and like to listen to. I don't have any artistic hangups, and will basically post anything I think will sell, but at the same time if I enjoy what I'm doing it's going to come through in the music. Simple is really the key word - most of the buyers that I know of are using my music as ambiance in the background of voice over work, so I try to be catchy and emotive but not intrusive, if that makes sense. That's just my style of music - if you're making complex orchestral soundtracks the target use may be just the opposite.
Okay, that was a bit rambling - maybe there's something useful in there somewhere. I am definitely in the infancy stages of self promotion, and am interested in what other people are finding return on investment in.
EDIT - Probably obvious, but another simple thing I try to do when on the forums or communicating with a buyer is to always be courteous and do the best I can to come off as professional in my emails/posts. We live in an age full of short hand, improper casing, and acronyms, so I figure if you take the time to write out full sentences you can really stand out. (Though for all I know I'm bugging people to death with my loquaciousness).