One of the reasons the music fits so well into the story is because Gunn included the songs in the script. So how did he go about deciding which ones would work best? The first thing he was looking for was accessibility. Essentially, he wanted the tracks to be semi-familiar — ones you recognize but might not be able to name off the top of your head (the only two songs that didn’t end up applying to were those by David Bowie and Jackson Five).
...
“I started the process by reading the Billboard charts for all of the top hits of the '70s,” explains Gunn. “I downloaded a few hundred songs, and from that made an iTunes playlist of about 120 songs, which fit the movie tonally. I would listen to the playlist on my speakers around the house — sometimes I would be inspired to create a scene around a song, and other times I had a scene that needed music and I would listen through the playlist, visualizing various songs, figuring out which would work the best.”
...
“When you see the characters strutting down the hallway to ‘Cherry Bomb,’ they were actually strutting down the hallway to ‘Cherry Bomb,’” says Gunn. “‘Ooh-Ooh-Child,’ ‘Hooked on a Feeling,’ ‘Come and Get Your Love,’ and more were all played on set by our marvelous sound team. I find it helps the actors and the camera operators to find the perfect groove for the shot.”