I write most of the music and about 60% of the lyrics and Kira, lead vocals, writes the other lyrics and nearly all the melodies.
Both of us use more than one method. For example, writing lyrics first and then the music and melody. Or the reverse, come up with the music and write the lyrics (less often). I think you should write in the way that best works for you and the song and sometimes that can change from day to day.
Here is the big thing: you must finish the song, partial songs aren’t songs, just ideas. I do have 50+ song lyrics sitting around and 15-20 bass lines as well. But most of the songs I write are new lyrics. And most of the bass lines are new. I will bring an idea I have written before into a song if it serves the song the best.
If Kira writes the lyrics, she usually has a melody in mind. First think I do is ask about the story behind the lyrics and what it means to her. I may not have the same experience she is writing about so I try to get as close as I can to hers.
Then, I pick the key it will be in, the tempo, and write the chord sequences for our 2 guitarists, and then the bass line. If I have any specific sounds/beats I want from drums I tell our drummer Brandon, who is great. He is so good I only do this occasionally. For example, in the song Delphi Raven (not to be confused with our band name…really!) I told him I did not want any snare, hi-hat, or cymbals at all in the opening, kick and toms only. I verbally gave him the beat idea and he created an even better one but with the sound I wanted for the song.
Last, I write this all down on a giant paper pad and mount it on an easel so everyone can read it. And we play, get input, play, get suggestions, repeat, until we have a working song. Off to the studio to record when we have 4 songs ready. Hear the mix and make final adjustments, add vocal tracks if needed, add instrument tracks to fit the song and the story. Tada! New Song. We average about 1 new one a month.
Themes are mostly emotion driven from real life events. So, breakups, bad partners, fears, anger, warning signs, losing a loved one, everyday life struggles, overworked, insomnia, substance abuse, and so on. We are called a “dark” band by many since we have few uplifting songs, but we do write them, just not often.