I haven't read the previous questions and answers about this topic, and I'm a relatively new member, but here is my take on the issue.
We need to make people aware of this site, specifically the community on popular forums, where the current information sharing is going on.
Forums are good for general communication and chit-chat, but not so good for getting reliable answers to questions.
I'm a bass player, and talkbass.com is my primary source of information about bass guitar, and music in general. Being an old an established community, you can find answers about pretty much anything about bass related. But, due to it being a forum, finding useful, reliable answers is pretty hard between all those trolls and random chat stuff and 'thanks', 'me too' posts.
Than there are ultimate-guitar, and harmony-central, and lots of others.
How can we do this?
Other SE sites has done some successful contests. Here is one from gaming.SE.
We can implement this format, and giving some reasonable prize. One contest may be about bass guitar, then the next one about electric guitar etc. Or about brands maybe? Like, Fender in general, or about stratocasters etc. I don't know if it is allowed, but we may get some sponsorship from a brand or music shop maybe?
Spreading the word about a contest is quite easy, given there is a appealing prize attached to it.
As I'm a bass guitar player, my examples are about related areas, and can be applied to all kinds of music.
- Answering questions at forums with relevant music.SE questions.
Pretty straightforward, but caution must be taken if the rules of the forum that we are posting allows this.
Wearing a music.SE shirt at music schools might generate some curiosity about the site?
Anyways, these are some basic ideas just popped to my mind.