If I'm learning a song, out comes the A4 pad and a pencil.
Firstly I'll identify all the sections (intro, verse, chorus, etc. - or whatever seem distinct sections) then five bar gate how many times they turn up, so I have a structure.
I usually write that out a bit more neatly - which helps me learn the structure - and then I'll start learning the actual bassline, annotating the structure I've written down with technical names like 'Fiddly bit in C', 'Flamenco !!', 'Goth Reggae', etc.
After all that's done it's practice time to get all the parts sounding right.
I don't usually explicitly work out the musical 'meaning' of the song - chords, key, etc. but I will occasionally as an exercise.
HTH