First, analyze the mood and message of the song. Then, look for elements that can be related to your comic's story or characters. Maybe a particular lyric stands out that can capture the essence of your comic.
Well, it depends on the song and the comic. Sometimes, you can just use the song's title as is if it works. Other times, you might need to get creative and play with the words or use a metaphor from the song.
You could take the song's main idea or a key phrase and tweak it to fit the comic's theme. For example, if the song is about love and your comic is too, you might use a relevant line.