The principles listed here are sound and helpful. If you follow them, your writing style will undoubtedly improve.
But do not adhere to them as rigid rules or you will suffer in your ability to express yourself. Passive voice exists for a reason. Long words can add variety, rhythm, and color to your prose. Elongated sentences can help give your writing a flow that a mere parade of short sentences can never hope to achieve, not even after a thousand rewrites. Or not. All such items can be misused as well, and the books are replete with bloated forms of expression used by lawyers, politicians, educators, administrators, and the like who would not know a simple word or sentence even if it stood before them doing somersaults. The key is to know sound principles for clear and concise writing and then to apply them with a rhythmic ear for balance in your forms of expression. That means, yes, use passive voice, long words, and flowing sentences as needed to add grace to your prose but always with the baseline in mind: that is, to communicate in ways that are clear and concise and that people will readily understand for your stated purpose (formal style for formal settings, casual for casual, and whatever fits for anything in between).
I note all this because, years ago, I consciously and diligently set about to attempt to master writing and stumbled upon the rock of "simplicity" during such stretches in my learning process where I had assumed that all one could do was follow such rules. Any attempt to apply such rules one-dimensionally is a mistake, and you will regret trying it. Follow sound principles, by all means, but not dogmatically.
The other major keys to good writing are depth of language skills and extensive reading. No one will read your work unless you have something helpful to say. You get this by working hard to develop your skills, and lots of writing (and reading) is vital to this process.
Much truth here. Years ago I took a summer school course in technical and scientific writing involving intense exercises in ruthlessly eliminating passive voice (regardless of the gymnastics involved in doing so) and many other common tropes of academic writing. The course was like a cell-obliterating chemotherapy against whatever creative writing voice I had managed to put together at that age, and it took years to overcome the effects.
Toss in a good measure of courses involving study of Hemingway and Vonnegut and I was a wreck for years. A passive construction, a ten-dollar word, the odd adverb--all had me in doubt and writing the most vanilla prose.
So it goes.
It was only when I started participating in NaNoWriMo that the forced march of cranking out 1666 words a night for a month combined with the permission to produce a shitty first draft allowed me to being my recovery.
Hemingway: Manuel drank his brandy. He felt sleepy himself. It was too hot to go out into the town. Besides there was nothing to do. He wanted to see Zurito. He would go to sleep while he waited.
Faulkner: He did not feel weak, he was merely luxuriating in that supremely gutful lassitude of convalescence in which time, hurry, doing, did not exist, the accumulating seconds and minutes and hours to which it its well state the body is slave both waking and sleeping, now reversed and time now the lip-server and mendicant to the body's pleasure instead of the body thrall to time's headlong course.
Reading this reminded me of some of the parallels one can make between writing and jazz. Ask any jazz musician and they will say that there are tons of "rules" and "suggestions" for what to play over specific harmonic movements. This is important, vital stuff for a jazz musician.
However, they will also say to forget all that and go beyond, because expression shouldn't be confined by rules.
I've always thought you abide by the rules just long enough to spot their usefulness and then your throw them out the window and create something new.
But do not adhere to them as rigid rules or you will suffer in your ability to express yourself. Passive voice exists for a reason. Long words can add variety, rhythm, and color to your prose. Elongated sentences can help give your writing a flow that a mere parade of short sentences can never hope to achieve, not even after a thousand rewrites. Or not. All such items can be misused as well, and the books are replete with bloated forms of expression used by lawyers, politicians, educators, administrators, and the like who would not know a simple word or sentence even if it stood before them doing somersaults. The key is to know sound principles for clear and concise writing and then to apply them with a rhythmic ear for balance in your forms of expression. That means, yes, use passive voice, long words, and flowing sentences as needed to add grace to your prose but always with the baseline in mind: that is, to communicate in ways that are clear and concise and that people will readily understand for your stated purpose (formal style for formal settings, casual for casual, and whatever fits for anything in between).
I note all this because, years ago, I consciously and diligently set about to attempt to master writing and stumbled upon the rock of "simplicity" during such stretches in my learning process where I had assumed that all one could do was follow such rules. Any attempt to apply such rules one-dimensionally is a mistake, and you will regret trying it. Follow sound principles, by all means, but not dogmatically.
The other major keys to good writing are depth of language skills and extensive reading. No one will read your work unless you have something helpful to say. You get this by working hard to develop your skills, and lots of writing (and reading) is vital to this process.