The five Ws are questions for gathering basic information: Who, What, Where, When, Why. Just like the five vowels include a "and sometimes 'y'", we could add 'How' to this list of questions words. Just iike Stravinsky, the more information I have regarding these topics, the easier it is for me to write a piece.
Who: Generally I need to have an idea of who will be singing or performing the composition I am to write. This will enable me to determine instrumentation and help identify the difficulty level. An amateur choir does not have the same musical skills as a professional octet, and if the brass ensemble is two trumpets and two trombones, writing a tuba or French horn part does not respect who the group is.
What: For choral pieces, what is the text? Is this a concert piece or a piece for worship? What addresses The answer to what sort of piece this is addresses the form the composition will take.
Where: Is this piece for a small church covered in carpet, a large resonant acoustic, or
Yankee Stadium? The performance venue can influence the style of writing or the form of the piece.
When: This can be a very critical question for style. How long until the performance? How many rehearsal will the group have. I always strive to write pieces that will be successful not simply in and of themselves, but for the performers as well. Giving a group with little rehearsal time a piece that is too difficult to learn only will result in either frustration, a poor performance, or even a cancellation. Not good.
Why: This question for we is the one most closely related to musical style. What sort of affect is desired or intended by the composition? Is this a piece meant to convey joy or grief? Anger or delight? Severity or lightheartedness? Music has a message to convey, and that message is the why of the piece.