Writing is no longer a mondo means of making money ever since Dr. Seuss passed away, but there is more to life than money. The yields of writing include but are not limited to glory, props, rep, and cramps. These are known as "The Big Four." However, money can be made from writing if you manage to write a lot of readable words that people will want to buy and own. I will show you how to do it. It's really not that difficult.
1. Put sex in it
People are busy and don't want to waste time reading something that doesn't provide some greater purpose. Sex is perhaps the meaning of life as we know it, as doing the dang thing leads to more life and more sex. See the pattern, Sherlock? First there was sex, then came writing. So whatever you choose to write, a fantasy adventure, a dictionary, hell, even a romance novel, make sure you have some sex in there to grab an audience. Also, be sure to spare no details about the sex. If you haven't had sex before, I am sort of a veteran of my bedroom and can provide some perspective. Use terms like, "oh, ah, yeah," and "I'm all set" to really generate some imagery.
2. Borrow ideas from accomplished writers
Writing is half the battle, the other quarters being research and lollygagging. Every aspiring writer should use the Google search engine to see what is trending in the world of literature, and implement their findings into their masterpieces-in-progress. Game of Thrones just ended, which means we need another fantasy juggernaut to tide us over until the next one gets here. You could be the one to do it. George R. R. Martin may never finish the GoT books because he was sidetracked with doing lines (of candy) in Hollywood, so you could even beat him at his own game and write the next books before he can finish them. You already know what happens because HBO showed everyone. Fun fact: George "Rest and Relaxation" Martin used a lot of sex in his writing and he got a TV show out of it. Elementary, my dear Watson.
3. Get on TV and talk about your book
News anchors and talk show hosts have nothing better to do than talk to people. In fact it's their job to question and argue. Networks won't let anchors go home to their families unless they meet their daily quota for interviews, so just schedule an interview with someone like Ellen DeGeneres or somebody on the Today show. They will let you talk about your book whether it's written or not. People will see you on TV and begin to want to read your book because you are on TV, meaning you have charisma and you are smart and beautiful. People will then want to buy your book, which means more money for you at some point. It's as easy as 2 plus 2, which equals 4, Newton.
4. Don't quit your day job (if you have benefits)
If you have a job with benefits, such as health insurance, retirement plans, and vacation time, don't quit your job. I REPEAT, DO NOT QUIT YOUR JOB IF YOU HAVE THOSE BENNIES. This isn't really writing advice, but a friendly suggestion to keep those benefits as long as you can. Perhaps you can snag different insurance if you start your own insurance company. But this article is about writing a bestseller, not starting a bestselling insurance company. One thing at a time, Aesop.
5. Go door-to-door selling your book
Perhaps the fastest and most efficient method to propelling a book to bestseller status is to oversee the selling process yourself. In my experience, people respond to the sound of doorbells. Pick a neighborhood near you with big expensive homes. Homeowners are nice and friendly because they don't pay rent, and will hear you out if you say you are selling a book. So grab a bunch of your books, a snack, and start ringing those doorbells, Melville. Protip: Spice things up by ringing the backdoor because most people are tired of answering the front door.
6. Have fun
Writing wasn't meant to be fun, but you should try to relax and enjoy writing your bestseller. Just think of all the money you will soon have, and all the fame of being an accomplished author. Oh, ah, yeah. Can you feel it, Hemingway?
With this knowledge in your brain you should be able to write a bestselling book in no time at all. A reasonable goal would be 3 months to 2 years depending on your current schedule. The sooner you start writing, the sooner the New York Times will call you and say, "congratulations [your name here], your book has sold enough copies to be a bestseller. The profits have been funneled to your bank account and your private jet is in the parking lot, with pistachios, not peanuts.