This advice is often phrased as “mistakes made by new writers”. I don’t like the word “mistakes” and I like to express thoughts in positive advice that people can do something with.
So what is the most important thing writers should be doing?
Well, duh, I can hear you say. But I see so many new writers not writing, and then lamenting that they haven’t sold anything and that they have no time.
You will never have any time if you don’t make the most important thing your number one priority.
In short: you will never be a writer if you don’t write.
You learn the craft by writing. Stop obsessing over writing rules or whether or not something is good enough. You learn through reading and writing, and when you’ve written, writing the next thing.
If you don’t write and finish your writing, you will never have anything to sell. The more things you have to sell, the more chance that you will actually, y’know, sell stuff.
Stop obsessing over things that are outside your control. For example reviews, if you’re self-published, or the tone and precise content of rejection letters if you’re trying the traditional route. STOP. OBSESSING. Obsessing isn’t getting any writing done.
Are your current works not doing as well as you’d hoped? Write something else.
Stop complaining. Shut up and WRITE!