The first thing you must do is to decide what type of writing you want to do. Do you want to write poetry, short stories, novels, magazine articles, etc?

Target Audience: You must know who your audience will be. Decide whether you want to write for men, women, children, teens, etc. If you are going to write for children, decide on which age group: babies, toddlers, preschoolers, young school age children, preteens, teens, or young adults. If you’re going to write for adults, there are various age groups there as well. Decide whether your writing will be technical, literary, informational, educational or mainstream. There are very few books that everyone will enjoy, so decide who your target audience will be, and then write your story with them in mind.

Think Like Your Audience: Once you know who your target audience will be, write with them in mind. Put yourself in their place and try to imagine what they would like to read. You should remember that a poem written for a six-year old will not be interesting to a twelve-year old, and a story written for an adult would probably be too complex for an eight-year old. Never talk down to your readers. Do not assume that readers are not mature enough, or educated enough, to understand what you have written. If you find yourself adding tons of explanations to clarify what you have written, then maybe you should consider rewriting it in a simpler manner.

Literary or Mainstream: Decide whether your story will be literary or mainstream. Speaking from my own reading experience, you don't have to set out to write a literary novel. Sometimes it just turns out that way. No matter what you write, literary types will probably find something literary in it, while others will simply read the story and enjoy it at face value.

Fiction or Non-fiction:Decide whether you are going to write fiction or non-fiction. Your choice will somewhat determine how much research you will need to do. Fiction stories are made up, but there is some research required because readers still expect information to be as accurate as possible, while in non-fiction, there is much more research required because everything must be accurate. In fiction, if you're going to write about a real place, then you need to research that particular place.

Personally, I prefer fiction. In fiction writing, there is more leeway allowed when it comes to grammar, especially in dialogue. Non-fiction must be grammatically correct.

Length: If possible, decide what length your story will be, although you may not know how long it will turn out in the end.  A story can be as short as a few simple words, or as long as several hundred pages. Short stories may be shorter than a novel, but that doesn't mean they're easier to write. Short stories must contain a beginning that will grab your reader's interest, and introduce the characters and conflict. They must also contain a middle that will lead up to the climax of the conflict, and then they must have a suitable ending to show how the conflict was resolved and by whom.

One Or More: Decide whether this story will be a standalone, part of a trilogy, or part of a continuing series. Many publishers prefer to buy books that are part of a trilogy, or a series, and fortunately, many characters are well suited to continuing roles. If you think you are up to writing a series of stories then you should try to develop characters with their continuing roles in mind. After all, you can't kill a character off in book one, and then have them punching out the bad guy in book three. Readers keep track of characters and they don't like when an author tries to slip something like that past them.