Ways Songs Produce Income

Music Licensing, Sync Opportunities, Radio play and Streaming are just a few ways that songs can produce income. An invaluable article on the subject from Kopywriting Kourse is by home-studio, musician/producer Joyce Kettering, who goes into considerable detail, outlining and comparing income streams and tracking the data generated over time
https://kopywritingkourse.com/how-to-make-money-with-music-licensing/

Another option is to sign up to the Creator Academy on Youtube to license your music directly onto their platform. https://creatoracademy.youtube.com/page/lesson/artist-monetization

Of course, if you are with a publisher, they will be looking for opportunities to have your music synced directly with TV shows, movies, advertisements etc. These can all pay quite well, although your publisher will generally take a 50% commission. However 50% of something is far more than 100% of nothing, so generally speaking, it’s still worth getting those opportunities from a trusted publisher. 

There are also laws that attempt to protect songwriters’ incomes (such as the Digital Millenium Copyright Act of 1998 and the recent Music Modernization Act 2018) and aim to improve income potential for songwriters and producers alike.  However, these aren’t in themselves income streams, but function more so in keeping the industry alive against indisputable changes in revenue within the music industry as a result of changes in consumer trends.