Why this is a mistake: Too often writers disconnect from the people on the other side of the writing (the readers); there’s a breakdown in effective communication.
Every type of written material is geared toward a certain type of reader. A technical writer has to know who the consumer of the manual would be. A writer for a magazine has to know what demographic that magazine targets. Genre fiction writers should know what type of readers gravitate toward that genre.
The solution: Study the end-product of your target publication, or the best-sellers of your chosen genre. If you want to write for magazines, study those magazines, their advertisers, and their core demographics. As a novelist, I go to bookstores and simply sit there and watch people who wander the stacks. Try it sometime. Watch how people select books. What stops them? What catches their eye? Is it the cover designs? Titles? The back cover copy that succinctly tells them what the story is about? Go online and watch chat groups of readers. See how they discuss books and how they feel about what they read. Always, always think about your audience, what they are reading and what they want to read.