Another way to promote is to be different. It may be tempting to follow trends, but originality is very important for relevancy and narrowing competition.
The last advice is go to the source. Record labels, managers, influencers; Don't beat around the bush. Usually the music industry has key people that "gate keep" and scout talent.
There are a lot of really talented artists that simply can't get on the surface of culture. That may be by design. We accept artist suggestions at rapindie@rapindie.com.