There are three things that need to be considered before a writer decides on a certain style:
1. What kind of style would be appropriate for the content that is being called for?
Sit down and think about what it is you’re writing about. Does it call for an impersonal style? Something informative? Or maybe it’s facetious and playful. What kind of audience are you writing for? Different pieces of writing require different styles that are more suitable for its subject matter.
2. Choose which elements of style you would like to use in your piece. The most commonly used are diction or word choice, syntax or sentence structure, and voice. The elements can also sometimes depend on whether your piece is fictional or nonfictional. They may slightly differ from each other, as nonfiction is more limited than fiction.
3. Determine which perspective to use. Will it be written in first person? Second person? Third-person omniscient? Will it be expository? Narrative? Persuasive? This step should be easy after mulling over which styles would be appropriate. Writing from a certain perspective really sets the tone for the piece. Is it objective or subjective?
After considering these three things, picking a specific style should come rather easily to you. It’s all about what’s suitable. Styles hardly ever remain constant, simply because the content is hardly ever the same.