Rather than describe the compositional process in romantic terms as music flowing through a composer to the audience, it is more useful to think of composition as a process that involves the composer working with materials using a collection of methods. Applying the same methods to different materials can lead to an entirely different composition. Likewise, applying different compositional methods to the same material could lead to different compositions.
We can break down the compositional process into four stages. Understanding how your thought process differs when you are working in the different stages is important, because behaviors appropriate to one stage may slow you down or produce poor results when used in another stage.
This stage is marked by a lot of trial and error, improvisation, and free association. You’re trying to generate material, and it is best to not make critical judgments at this stage. You want a reservoir of potential ideas. The precomposition stage can also refer to the gathering of materials to focus the composition. Often the word is used to refer to the systemization of material, but this approach is not the only focus in this stage.
Composition takes the collection of material, of possibilities, and works towards fixing this information into fixed form. The process of discovery is still applicable, but discovery tends to take place in the realm of implications derived from the material. We speak of intention. Often the composition stage moves from sketches, through multiple drafts, to a final draft. Critical judgment increases throughout this process. Editing continues even after the completion of the work, to refine details, corrects errors, and/or supply obvious omissions.
Realization involves most obviously performance of the composition. Performance involves rehearsal. Through the rehearsal process, the composer can further refine the score and/or parts to more closely articulate ideas from the previous stages. Editing still takes place, but it is much more focused on refinement, solving problems where the composition is perceived to not meet the intentions of the previous stages.
Evaluation is part of all the previous stages, but at this point the evaluation serves the purpose of a complete assessment. The composer (and teacher) can work to find areas of success, to make any further (hopefully minor) changes to the existing piece, and to refine your techniques and behaviors from the previous stages as you undertake new compositions.