Writing is a mysterious process because it involves both intellect and intuition. While essential things like grammar, formulaic plot and character development, and basic composition can be taught in a classroom (online or otherwise), the underlying passion fueling the narrative is a completely organic function.
First of all, not every writer has the same agenda. They also greatly differ in terms of inspiration sources. This is simply because every writer, like every human being, is a unique individual. This quality is what separates him or her from being mistaken for any other voice in the global literary chorus.
Only you know when something doesn’t “sound” like “you.” An editor that is familiar with your style can actually help you sustain that natural rhythm, rather than trying to alter it for the purposes of the publication’s perimeters.
There are cases when your innate sensibilities simply do not match the assignment at hand. If you expect to keep getting hired for your services as a professional wordsmith, you will need to adjust accordingly, all ego aside. This means whatever the editor wants, the editor gets. The editor is always right if you’re getting paid to contribute. It’s a job, not a personal platform.
If you’re self-publishing, then your main guide is your own artistic conscience. You should add some beta readers to the mix as well, just to make sure you’re not being overly self-indulgent, which can turn off your readers, the ultimate arbiters of commercial literature these days.
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Just like with Facebook updates or tweets (especially when inebriated, emotional, exhausted, or all three), you need to be very careful with your tone of voice, not just your choice of words, in order to avoid misinterpretation of your intended meaning. Again, this often is a matter of both personal restraint and objective processing of subjective material, at least if you're planning to share it with the general public.
The best way to self-edit, I’ve found, is to simply read your manuscript back to yourself out loud. Though tedious, this is the most effective and efficient way to discover typos, find out if you’ve skipped a word in a sentence, or whether your choice of syntax and sentence structure simply comes off as awkward and amateurish.
Even then, you’re relying on purely subjective instincts. These can be deceptive. That’s why it’s always recommended to get a second, third and even fourth opinion on your work before putting it out there.
However, you are the final judge. If your words “feel” right to you, trust yourself, at least if you’re comfortable with your own experience as a published author, whether you’re independent or traditional or both (the latter increasingly becoming the norm).
The key to authorial authenticity is to stay true to your own voice whenever possible. The only “wrong” words are those that come off as forced or false. You will feel it in your gut if your words ring true or are sloppily contrived, as if plagiarized from the common consciousness, expediently concocted for the mere sake of filling blank space.
Many writers need to write and rewrite in order to find the right words. Others nail it right away, but second-guess themselves. In either case, have faith in your own honesty.
By and large, readers appreciate and respond more positively to well-crafted sincerity more than polished but soullessly calculated expertise. And other than your own, those are the opinions that ultimately matter the most when it comes to your work. Nobody likes a phony.