I will say this, though - one of the best blog posts I've seen was one that recommended picking the right genre if you want to sell well. I experimented for a couple of years, trying niche after niche until I found what worked for me. And what works for me isn't necessarily what's going to work for others. However, if you want to make it in fiction - I'd say study the Amazon top 100 fiction bestseller list, and see what ends up there again and again, for a start.
Anyway, I got a lot out of the Warrior Forum back in the day, so here's some free info.
1.)The main key to my success, other than the fact that I'm a good writer, is that I write books in popular genres. And I took the time to get to know those genres. I have read many bestsellers in those genres, studied them, analyzed the beginning of the books so I'd know how to write a compelling opening right away, I'd analyze the characteristics and descriptions of the hero and/or the heroine; I'd break down the plot line, the call to action, the complication facing the hero or heroine, the "all is lost" moment, how the protagonist overcomes the "all is lost" moment...So, this was a "get rich very slowly and with a lot of time consuming effort" kinda deal.
2.) I sit down and write out an outline before I start writing. This takes me several days, at least. I figure out who the hero and or heroine is, what problem they are facing, who the villain is, why the villain is doing what he or she is doing, what the protag's "dark night of the soul" moment is, how they will overcome it, and the ending of the story.
Then, I write out a chapter by chapter outline, with a few paragraphs for each chapter.
Then, I set my cell phone timer. I find that working in short 20 to 30 minute bursts is most effective. I write anywhere from 600 to 1200 words in that time period - because I already know what's going to happen. Before I started pre-planning my stories, writing took forever, and I frequently abandoned my stories half way through.
I take a break after each writing mini session, but a short break.
I do at least four sessions a day, sometimes eight. I write almost every day. Usually six days a week. Sometimes every day for 10 or 15 days straight.
I start in the morning. That way even if I have errands and the rest of the day gets away from me, I've always gotten a few thousand words done before I head out.
Within a couple of weeks, I have a rough draft. Set it aside for a few days while plotting out the next book. Go back, revise and add a lot of detail and look for typos. Send it out to a copy editor.
Voila. New full length fiction book every month.