The first thing I usually get asked as a composer is, where do you start when you write a new piece? Unfortunately there is no definitive answer to that question as each piece is uniquely different. In my second ballet, La Feuille Qui Tombe, I started writing 3 minuets into the overture specifically for bassoon, clarinet and cello, but for my massive tone poem Levensverhaal I started halfway through the second of two parts with a solo organ. Needless to say there is no set way to write a piece of music. This however doesn't mean I can't walk you through the necessary steps.
The most important things as well as the first things you need are an idea and a reason. A reason to write, weather it's a commission or a need to express, writing music for the sake of writing music never ends in a solid or satisfying product. The second thing, an idea, is the much more creative aspect. This can be compared to a painter choosing his or her colours and brushes, as well as a rough idea of what the painting might look like in the end. The founding ideas regard your choice of instrumentation, style, genre and feel. Weather you want a philharmonic orchestra or a string quartet, a waltz or a ballet, something slow and sad or fast and angry, the founding idea is what kickstarts the whole piece.
Now that you have a general idea of what you want instrumentation and genre/feel wise, you need to develop a theme or multiple themes. If it's a ballet, opera or musical, maybe have a theme for important characters, if it's a symphonic or orchestral work maybe decide your principal subject. Once you have your melodies you just put a chord progression to it. It's helpful if you can put more then one, specifically in the relative major or minor key so you can have different statements of the melody and theme with different supporting harmonic content.
Within melody and harmony down pat, you have to figure out ways to turn the harmony outlined in the chord progression into proper accompaniment. For example, classical Mozart arpeggiation or Beethoven big tuti chords, perhaps rippling arpeggios from Smetana, or something a little more erratic like atonal Stravinsky, Sherker or Brain.
With a melody and accompaniment down pat, now the final structuring can take place. This is mainly the developing of the melody over varying harmonic and rhythmic backgrounds as well as incorporating new melodies and counter melodies.
All thats left is an intro before all of that, and a recapitulation of the melody at the end before a finale and you have yourself a piece. This however may be easier then it sounds.
The introduction is the first thing the audience will hear. It sets the tone and their expectations for the rest of the piece. Believe it or not, this has quite a significant impact. The psychologically preconceived notion an audience member has going into a piece or a concert will undoubtedly effect their resulting opinion. A negative initial perception results in a more negative experience and visa versa. Therefore it is absolutely imperative to write an introduction that does your piece justice.
Similarly the finale is equally as important as it is the last thing the audience hears. Leaving a good impression is just as important as the first impression. I've once been told that "The beginning and ending of a piece are the most important, the middle could be rubbish but we would still love the whole piece as long as we hear it in context." Sadly I do not believe this to be true either. There is no way to cut corners here. The only way to have a good result is to write something great through and through. Simply put great thought into every aspect of the piece to make it the best possible version it can be.
For more specific questions, contact my at my website: https://www.aidanmtaylor.com
To hear about my personal process, read my article "My process for writing music".