Music

A bit of music during the opening credits can help set the mood of your book. If you use music, you have to respect copyrights. A snippet of a popular song by a popular group is not going to qualify as fair use. Permission by the performer is not the same as permission by the original author of the music, so you can't use your friend's rock band to perform someone else's music.

If you decide to add music, make sure the playback volume level matches the voice volume level, neither too loud or too soft. You don't want to suddenly blast your listener's eardrums. Don't make the music so loud that it drowns out the voice. A gradual fade out (done during editing) is better than abruptly stopping the music.