I knew about the 50MB APK limit at the start, but I was hoping CocoonJS fixes its memory management by the time I finish my game... but they didn't so i had to go back and remove a lot of assets.
Music files tend to use a lot of space, but if you publish for Android only, when you export from C2, unpack the zip, delete all the .MP4 sounds and keep the .OGG only, then zip it, and run it through CocoonJS, it works fine without the MP4 and should save u a lot of space on the APK.
As for tutorial, with C2 not that I know of. But the point is do not exceed 40MB on your C2 export, because you will need 10X the ram on loading the app with CocoonJS. Most phones are still less than 1GB ram which will not run it due to high ram usage.