Depending on where you live, if you have a local radio with reasonable reach and a varied taste in music, it is an incredibly powerful resource. The good thing about local radio as opposed to internet outlets is that the level of entry isn't as high, not suggesting your music can be shitty as it should be implied that good music is the minimum req for any promo to be worth it, but with big youtube channels you're often competing with others who are equally skilled and at that point most of them tend to lean towards the guy who already has an impressive online history and a bit of hype to his name. A friend of mine started on this local radio here, and because he managed to get onto the tropical house train before it got ultra saturated, his music really took off, couple months after being aired on radio he got a feature on TSIS and now vogue. So local radio if you can, the other approach is the classic bootleg, a good bootleg at the right time sells itself, also remix contests which is more or less the same thing, though it generally has a smaller potential pool of listeners but that evens out somewhat because there's more hype around it (if you win). Others have suggested youtube, soundcloud and blog promoters so I'm not gonna touch on those, and personally I'm not really a fan, I think they are overly saturated so unless you start really small the chances of them actually seeing your submission amongst the 100s of submissions they get every single day can be very hit and miss, but you shouldn't dismiss them though, send your music to all your favorite online outlets as well because while a little 50-50 it takes about 2 minutes to send them your tunes.