Of course, that's what we composers, at least this one, don't do. When I am writing a piece of music it is not, oddly enough, about myself; I am not composing myself. I talk about the belief that music is somehow the autobiography of the composer in this post.
Instead, what I am doing is composing something for someone. I am writing a string quartet at the moment and it is for a quartet of string players. I would like to give them something to play that might be different from the other pieces they play.
I was talking to a friend of mine, a viola player, about what goes through people's heads when they listen to music. A lot of people imagine natural scenes or other things from daily life: "that sounds like waterfalls" or "a busy street scene". There are certainly pieces that suggest that kind of thing, Debussy's La Mer of course, suggests the ocean. But when I listen to music, if I am really paying attention, I am following the "argument", the way certain elements are handled, how the composer solves certain problems. My friend said, "yes, that's how composers look at things"! Performers perhaps listen to how the players handle certain technical problems or what timbre they project, or how they phrase.
So, in deciding to write a string quartet, I have a number of problems to solve. Should it be, as most are, in multiple movements? If so, how many? Beethoven usually wrote in four movements, but there are quartets of his that have up to seven movements. Shostakovich usually wrote in four movements, but one quartet is in a single movement and one is in six movements and another in seven movements. I'll probably opt for three or four movements. The kind of "standard model" is for a fairly up-tempo first movement that has some substance to it, a slow lyrical or dramatic movement, a quick movement like a scherzo that might be diversion and a final movement that is dance-like. There are numerous exceptions to all of these, of course! You might, as Bartok did, go for an arch-form in five movements. In some of Beethoven's and even more, Shostakovich's, quartets, there is more the feeling of a suite of movements, each with a different character. I might opt for that, simply because I have been exploring that kind of structure in a couple of pieces for solo guitar that I have recently written. I like that alternative because, frankly, I really don't feel any affinity at all with sonata form!
Sonata form in the Classic sense, is structured using harmonic means: there is a tonic key with its themes and contrasting themes in a contrasting key. Then the form achieves completion by returning the themes all in the tonic key. Lots of exceptions to this, of course, but that's the basic idea. Trouble is, my approach to harmony doesn't really work that way. So what I will probably do is more Baroque in concept: a suite of contrasting movements.
I usually start with some little idea, a fragment or a chord or a rhythm and then put together a piece from there. But this time, I'm doing a little more pre-compositional planning. Shostakovich's first quartet apparently was the result of some "compositional studies" and only fortuitously resulted in a completed quartet. Well, enough of my meanderings. Why don't we listen to that quartet? Here is Shostakovich's String Quartet no 1 in C major, op 49 played by the Emerson Quartet. Each movement is a separate clip: