What do I want to say on this subject?
What am I trying to accomplish in writing about it?
Who are my readers? What sort of people are they? What are their tastes and interests, their values and prejudices?
How can I make them share what I think and feel about my subject? Should I tell them outright what my convictions are, or should I simply put before them the evidence that has impressed me and invite them to form their own opinions?
Shall I treat the subject seriously, or are my readers the kind who respond best to a humorous approach? Shall I write as if I'm addressing them from a lecture platform, or shall I try for the style and tone of an evening of good talk with old friends?
Questions like these are the big questions in writing, the ones you need to face up to first when you set about planning and drafting a paper, the ones you need to keep steadily in mind as you write and rewrite. Essentially they are questions of rhetoric -- how to find, organize, and present your ideas so as to achieve a specific purpose as you address a specific audience on a specific topic.
-- from the Introduction of Index to English, Sixth Edition