1. For music, use music streaming services like Spotify, they allow you to listen to all your favourite songs without taking up space in your phone. (It does use the internet though, not recommended for people who have little data included in their plan)
2. On certain Android devices, buy a SD card to expand the storage of the phone.
3. If you need some storage immediately, try clearing out the "cache" in apps that you generally browse in, or download an "cleaner" app and it'll do it for you.
4. Go through your list of apps once in a while to uninstall apps that you no longer use so save storage.