While you may never have thought about it before, any song (or bit of content, really) can become relevant again on certain days of the year or when special dates return.
The easiest example of this would be an anniversary. Keep track of the exact date when you released every single, album, and music video, and then when this date rolls around again, why not celebrate your work of art once again?
You don’t need to do this with literally every song you’ve ever shared every year because it would quickly become tiring both for you and for those who follow you, but it can be a fun way to not only look back at what you have created but to reminisce. Time will pass by faster than you realize. While this is a plan to get more out of the music you’ve already created, you’ll probably end up being glad you put this schedule into effect as it will be wonderful to revisit older tunes.
When reposting songs and videos on anniversaries, try to make things seem relevant and fresh. If you simply post a track and remind people it has been another year, they likely will not be interested enough to click it.
Also, it’s great to sprinkle in some variety when honoring anniversaries. One song may be a year old, while next week’s anniversary post could be celebrating a demo you released five years back. It will obviously take time for you to build up the kind of lengthy, time-tested catalog where you can pull this off, but it’s a wonderful way to subtly remind people you have been doing this for a long time.
From the moment you release a song into the world, it can make you money forever. Sure, you might collect the bulk of the cash a track will earn you in the beginning, but that doesn’t mean it ceases to be valuable after a few months have gone by.