Legal
Artist information from USPTO.gov https://www.uspto.gov/learning-and-resources/ip-policy/musicians-and-artists-profile
Free legal help for artists https://vlaa.org/get-help/other-vlas/
Mixing and Mastering
Getting the right loudness levels https://www.masteringthemix.com/blogs/learn/76296773-mastering-audio-for-soundcloud-itunes-spotify-and-youtube
Pitching music to playlist editors https://support.spotify.com/us/artists/article/pitching-music-to-playlist-editors/