This is a very big question. I think that many tend to forget that you are competing against labels and setups that are pretty professional when it comes to promoting music. Having said that, there are several areas that you need to have covered
The things I’m trying to focus on are the following:
What genre you will be working on, the more you stick to one genre, the easier it will be to develop your promotion plan
Create your Brand/Story.
Playlist Research, you need to find out several things; First is to understand which ones are the most relevant, but you must also look for medium sized and smaller Playlists since they many times are owned by artists working un the same genre. This will be useful since you will be able to learn about the Playlist Habitat with its hierarchy and interactions. During this process remember that there are persons behind every Playlist.
Research for relevant Bloggers working the genre, these will be the persons you will be pitching both your music and your story to.
Create and promote your own Playlist, in order to start mingling with other Playlists you need to start creating your own playlist and promote it. Something that works great is collaborating with artists in your genre and exchange songs. In other words; what you are doing is putting likeminded followers in the same sack for a period of time.
This process is not fast, I’ve been doing it for around 6 moths and I am learning every day. At present I have reached 400 followers in Spotify and around 100.000 Streams counting all the outlets (Spotify, Youtube Music, Amazon, Apple Music, etc…). I am continuously targeting in the range of 100 playlists each time I launch a single and plan to get this figure up to at least 300 Playlists over time.
If you want to kickstart your Playlist research I recommend that you acquire The Indy Bible for Spotify Playlists. You will not be able to get your complete list you want to target from them but its a good start.
I have my doubts about how effective a YouTube channel is for promoting your music. Bear in mind that they have opened YouTube Music and there will be a period of transition until they get all the music viewers form the traditional Youtube Channel to YouTube Music. I recommend that you focus your efforts in Spotify since they are the only outlet that has managed to get the Playlisting going and are openly working on means to help Independent musicians promote themselves in their platform.
You will also find quite a lot of literature related to the world of Playlisting. My favourite is “Work Hard Playlist Hard” by Mike Warner.
I hope this helps,