Submit your song to correct playlists. If you submit your song to the wrong playlist, you will waste your free credits and miss your chance on being added.
Only look for green, "Active recently" playlists, since those guys are most likely online at all times.
OPTIONAL: Sort by lowest followers first, since those are smaller playlists that artists most likely aren't submiting to, so your chances of being added are much bigger.
Repeat this step every week, because the credits are being reset every Monday. After few months, if your song is being added to the playlists, your monthly listeners should start growing.
If you have any questions regarding this, or you wanna hear professional feedback on your music, how to improve and get professional sound, get mix & mastering, send me an email on firstname.lastname@example.org, or hit me up on Instagram - @vordabeatzz