A high school student asked me through Facebook, “When you start writing a piece, do you start with the melody line, a form of accompaniment, a thematic concept, a short musical idea to elaborate on, or something different all together?” Here’s my reply.
What a big question! When I start composing, I often try to start with a vision of the piece, being performed by the intended ensemble. Since I generally work with choirs, my next step is to know the text (and tune if I’m arranging). Finally, when I’m ready, I’ll sketch out a vision for the piece, with number of measures, sets of double bars, intended timbre/voicing, possibly rhythmic ideas. Everything but actual notes. Only after the sketch is complete and pretty clear will I begin notating.
Other times I sit at the piano and find harmonies to sing over, or make up melodies and write them down.
Alice Parker has two fabulous books on her compositional approach that I highly recommend: Anatomy of Melody and The Answering Voice. There are also some excellent interviews in the book Composers on Composing for Choir (and there are several similar volumes with band composers.)
Finally, I think mindset is of the utmost importance. I subscribe to a literary view of composing that doesn’t seem too widely held in the composition world. I prefer to write without judgement and then edit without mercy.
The truth is, though, process isn’t as important as we think. My process won’t work for anyone else with adaptation. So, sure, find out what other people do, but also try things and see what works for YOU.