Release your music for free (with the pay what you want option if need be). If people like it, they can share it through social media and word of mouth which is how a lot of my music got around I think.
PLAY SHOWS, PLAY SHOWS, PLAY SHOWS, PLAY SHOWS, PLAY SHOWS.
Don't resort to too much gimmicky online promotion shit.
If you can't pull your music off live then you can't perform and/or the music isn't up to standard.
This couldn't be more wrong, I've seen bands accumulate more fans from a single music video than 20 gigs. Likewise I've seen bands sell out gigs just on the basis of a single EP.
Online PR is pretty much the only PR at the moment, people usually go to a gig because they want to see your songs and if they are there for the other bands then you rarely will get any crossover fans because people get excited at gigs about an interest that has already be established. The only people that become "fans" of your band at gigs are usually other musicians and that's so they can make sure you come to watch their shitty band and vice versa.
In decades past the reversal was true but that was back when there wasn't twenty gigs on every night about town and when live music had an appeal as something that wasn't super prevalent ie there was more of a mystique about it + there wasnt as high a prevalence of bum rate musicians playing chinese made instruments and you actually had to qualify your ability somewhat to get up on stage - ie not everyone was a fucking rockstar prima donna playing to a crowd of their mates.
These days I really think to get peoples interests you have to give them a good qualifying reason first and that needs to be delivered by way of good imagery, good songs and overall nice presentation of material and concepts. Playing any shitty gig you get your hands on is a good way to burn the fuck out playing to wasters in other bands.
We have been just promoting through friends and Facebook. It helps that we really don't care what happens, but it also helps when you have some fairly popular friends standing behind your shitty music...
Right now, I'm playing in a cover band and have effectively sold out as a musician.
I think playing live would be a key component that I'm missing. I can sing quite well when I have multiple takes- doing it live however is a whole nother beast.