Authorship is for the rich and famous (or what budding writers thought so). Some have noble visions, as they want their works to touch someone's heart. It seems like a stretch. You want to write a book because you want to say something on a particular subject. Ernest Hemingway, for instance, wrote a novel on bullfighting. Agatha Christie's works revolve around nasty murder cases. And Douglas Adams pondered on the meaning of life. (How many roads must a man walk down? Forty-two.) You won't run out of topics, but you must consider another thing. You're supposed to write for a particular group of readers.
A literary genre will narrow down your audience, but most writers have blurred the lines on literary genres. (A mash-up or crisscross is preferred nowadays.) It will be a waste of time to think about it, as you must finish it sooner or later. It may not be a bestseller. It may not be noticed at all. It shouldn't darken your thoughts, if not turn you into a bitter person. After all, you want to write a book.
You figure out the reasons for wanting a write a book. The next step is to know the rules. If you're thinking about what you have learned in college (like how to write an abstract), then you're dead wrong. It will take more than your accumulated knowledge (during the last few years in the university). If you read too many novels, then you have a clue. Make it five.
5 Rules to Live By
Get to the action immediately. You've been thinking of devoting the first chapter on your setting. You want to describe a certain place with great detail without leaving anything behind. Unless you'll use that place as a metaphor (like what Dan Simmons would do with the Arctic region in "The Terror"), then it will be better to limit your description to a few sentences. The same rules apply to weather. You can save it for the middle part, which will serve as your turning point. (Recall Bram Stoker's hair-raising narrative about the arrival of the Demeter in Whitby.) The first chapter must give a general idea about your book. Putting it in another way, so many writers have described a place. It's more or less the same. Find a spot to stand on, which offers a perspective.
Don't dwell on the characters. If you know your classics, then you're aware that the novels with the main character's name in the title aren't about that person. It's complicated, which should hold the reader's attention. One sentence can be sufficient, as a certain feature of the character will shed a light on what the book is all about. If you're at a loss, then think of a familiar figure. Name one special thing about that person.
Remind yourself of those pages that readers skip (until the final chapter). You must have used adverbs one too many. You forgot the golden rule about exclamation point. (Use it a few times per 100,000 words.) You have introduced many subplots, which stray you from the main story. Your readers must have seen it all, but you have something up your sleeves. Length hardly matters here. (A ten-page short story can pose more challenges, though.) In this regard, you should have an outline to keep you in the right direction. It might take you a month to finish a book, it can last a year. You can go back to your outline from time to time. If something is wrong, then go back to the very start. Think about changing it.
It's fine to change your mind. A better idea might come along sooner than you think, and you won't realize it while you're lost in the woods. Keep on writing until you're too exhausted from it. Don't ever think of proofreading your draft, as you don't want to interrupt your flow of ideas. If it's getting difficult for you, then postpone your writing for another day or two. It's all about perseverance, even if there aren't any (employment) benefits attached to it.
The rest of the rules doesn't matter anymore, as you only need self-assurance. It seems to mirror life, but creativity allows you to write whatever you see it. Try to write it honestly, if not as accurate as you can. It will help you to do what is needed to be written.
The Hard Truth About Writing
It will only be natural to ask the opinion of others especially those who have been writing for years. Take it with a grain of salt. (The writer may be manipulating you, as you might have more promise than anyone of recent. Another writer may be burned out, revealing bitter thoughts. And it can be contagious to anyone.) On the other hand, asking questions doesn't imply that you have doubts about your capabilities. Always be confident of the story that you're about to tell your readers, even if it's a prose on the cultural impact of a toilet.
You must learn to love writing. It will alleviate the misery that you feel during those lonely moments, not to mention the possibility that your effort won't be rewarded at all. The feeling isn't mutual, though. It doesn't matter if your characters may not give you a sympathetic hug while your prose might not put you in a better place. There won't be any shortage of generosity, though. Don't speak ill of your craft.
You won't be a better writer if you have limited vocabulary. Keep a dictionary beside you, if not a thesaurus. Moreover, reading is not a hobby for the likes of you. It's a necessity.