What do you need?

Question

What do you need to start writing a book? Besides and idea.

Answer 1

A computer would help a lot.
But most importantly what you need is the burning desire to write, the dedication to keep at it, the perseverance not to get discouraged, the talent to write well and the time to devote to the task.
You need a schedule that you'll adhere faithfully to, writing for at least a few hours every day.
Most of all, perhaps, you need to believe in yourself, to know that you CAN do it.

Answer 2

Often, the book writes itself. But you have to have the focus and mental energy to committ to doing it.
Many authors devote the "best" hours of their days, that is, early morning, to going right to writing.

This may involve a lot of sacrifice---home chores, work, money, time, etc. It may take 6 months, it may take a year.
Great authors (and other great artists) often committ totally to their work at the expense of every one and every thing in their lives.

The idea will drive the writing if you let it----you may need to do practical research, or simply give yourself time to let your subconcious plan the book for you--this is a world where you have control of everything, but a world that must be built slowly. There may be some false starts at the beginning, but keep at it. If you are including characters, they often "show up" on their own, and wait for you to put their lives down on the page. Agatha Christie, for example, based Miss Marple on her own Grandmother, but had no idea where Hercule Poirot came from in her writing---he just appeared, and she wrote his adventures.
But most of all, it takes time and effort and respect for your ideas.....Jean Auel (author of CLAN OF THE CAVE BEAR) took a year off her job and all her housework, with her husband's support, did intense research, and started writing her 5-book series at her kitchen table.
Ernest Hemingway wrote a lot about "writing" (as did Stephen King)...he suggested only thinking about what you are writing that day, and not thinking ahead in your story, to keep the suspense and excitement fresh.