Maybe you want to write or maybe you are required to write; either way, you must first understand who your audience is to determine how to approach the project.
If you initiate the writing, you must determine your audience. Will your words be meant for you alone or is this project one you hope others will read and enjoy? If it’s for you alone, just bang away on your keyboard or splash cursive (or print) musings all over blank pages. Don’t worry about grammar or punctuation; heck, don’t even worry about coherency. And conciseness? Pfft! This is called journaling.
But, if you are writing for others to read, you must evaluate who that will be. It’s not as hard as it seems. Yes, the people who you hope will read your words are diverse. They will also have some commonalities.
If you are writing for academia or business, you have a fairly clear audience: in academia, your professor and fellow students; in business, your boss and coworkers. You can generally assess the education of these audiences, their needs and expectations. How you write much of what you write will be determined for you. The structure, word choices, grammar and punctuation will be dictated by that audience. In either case, you are conveying information and must convey that information in a manner that is consistent with the rules established by that institution. In academia, the writing style is dictated by the style guide chosen by the school or instructor. Some businesses also follow the guidance of a particular style guide, but even if they don’t, the culture of the organization determines the formality or informality of written communications.
If you are writing for a particular publication, actually read the publication and find that publication’s writer’s guidelines. Both will give you a lot of information related to its audience. When reading the publication, notice the word choices, tone, person, and content. Without plagiarizing (do I even have to say that?), mirror those in your own writing. Most writer’s guidelines are online, but if not, find them – even if you have to contact the publication and ask for them. Then follow the guidelines.
If you are writing fiction or nonfiction, determining your audience may take a little more time, but it’s fairly straightforward. First, read in the genre you intent to write. Next, read more in the genre you intend to write. In the books you are reading, find the Acknowledgements or Writer’s Notes pages. Often, you’ll find the author’s agent and editor. Research other books and authors they have been involved with. Get the sales figures on those books. How big is the audience? Read online and printed reviews of the books. Who likes them? Who doesn’t? You will begin to get a sense of who the audience is for the genre that interests you.