When I began writing, I chose one song for each character that represented their mental state or their personality in some way. When writing each chapter, I threw the songs for those characters into a playlist so I'd keep their personalities consistent while I typed.
Here's the playlist, if you'd like to check it out! I'll be doing this for each Part, either upon completion or at the beginning.
The Shadow- "Main Title (Theme from 'Jaws')"- John Williams
Bucky- "Thief"- Imagine Dragons
Clint- "Men in Tights"- Robin Hood: Men in Tights
Morris- "Enter Sandman"- Metallica
Tony- "Adventure Awaits/A Heroes Journey"- Galavant Soundtrack
Inessa- White noise from an old VCR (I didn't actually put this in any playlist)
Thor- "Secret Mission"- Galavant Soundtrack (I have no idea why this makes me think of him, originally it was Tony's song)
Dennisson- "My Bloody Valentine"- Good Charlotte
Steve- "The Weight of Living: Part 2" - Bastille
Banner- "Oceano"- Josh Groban
Natasha- "Inama Nushif"- Children of Dune soundtrack
Sam- "Thriller"- Michael Jackson
Hulk- "Dovahkiin/Song of the Dragonborn"- Skyrim Soundtrack