If You Want To Learn How To Write Fiction, Study The Novels You Love To Read
You can take writing classes at the local university that presumably will teach you how to write fiction. I know you can do this because I have taken many such classes. And I definitely did learn things about writing that were helpful. But they don't really teach you how to actually have the confidence to begin writing and go on to complete a first novel.
If you are a voracious reader you already know exactly how to write a book. First of all, you should only think of writing something that you enjoy reading. In other words, do not attempt to write a science fiction novel if you only read historical romance. By the same token, readers of fantasy should probably stick to that field.
The reason is that you want to remain true to your reader. It may be that you can earn more writing out of your genre, but your reader will see through this. What you need to do is, when you find a book that you love and you get to the end of it, begin reading again from the start and this time take notes. Basically dissect the novel and figure out how the author wrote it. Did he write in first or third person, what type of setting, what was the conflict, what made you (the reader) care about the main character, and so forth.
When you get to the end of your second reading, you will have completely mapped out this novel. Further, it is a book you loved to read, and a subject you would probably enjoy writing about.
Do this four or five times, and you will have taught yourself how to write fiction of any type. At this time you should put down the books, turn on the computer, and begin your own novel. That's right, you are ready because you have learned exactly what you need to know to complete a manuscript.