Finish every manuscript you start. Set a word goal and meet it every single day. Show, don't tell. Don't use adverbs. Read everything in sight. Write what you know.
Any of that sound familiar? I'm pretty sure it does. These are respected tenets of the writing community. Their certainty is almost comforting, in a way.
Here's a nasty little secret - statistics mean nothing to the individual.
Most writing advice is well-meaning and comes from a good place. Obviously if you never finish a manuscript, it's at least 30% harder to sell your book. Reading a genre is unquestionably the best way to know what other readers are expecting.
But there are no absolutes. Not in writing, not in life.
Writers are passionate people and you will find folks all over the internet and the real world arguing vehemently for one side or the other on these and other issues. People will absolutely insist that vampire books are dead(heh), or self-publishing is a fool's game, or that you cannot use a prologue.
These people don't know you. These people don't know your book.
All too often I'll see writers asking for not just advice, but judgement - "Is this story idea a good one?" "Is it okay to talk about this topic?" "Is it alright to break genre convention in this instance?"
Folks, you are the pale moon and the golden sun of your writing world. Nobody else can tell you in certainty that a character or a plot or a book will or will not appeal to readers. If that were possible, we would all be bowing at the feet of Random Schuster Harper Disney and its one employee.
There's nothing wrong with taking advice. At least considering the advice of others is not just a good way to write, but a good way to live. There are limits, though. All things in moderation. The advice of other writers cannot write, edit, or save your book.
You are the master of your destiny. Accept no substitutes.