There are many benefits to one’s personal development in writing. In general, I feel that writing cultivates worthy habits, behavior and characteristics. These are strong self-discipline, self-confidence, clarity of expression, and a constant awareness of what is around you.
A good writer will have good self-discipline. This is critical in regulating your time in a consistent manner to allow for progress, however incremental, in your writing. Self-discipline also creates good personal habits. We live in an increasingly digital world of needless distractions that nibble away at our time. It takes discipline to counter this. This is especially true if you essentially have your entire day free to write.
An effective writer must be able to distill complex thoughts into easily understood plain language yet not rob it of its punch. It is the idea that matters, not the words. It is not a case of overestimating the average reader’s intelligence. Rather, it not writing in a manner that is needlessly complex. Constantly working at this not only makes you a better writer, it makes you a better speaker. Years of teaching astronomy to undergraduates who were not science majors taught me that effective teaching makes something less complex without watering it down. It also means when you have said enough, say no more.
When you are working on a novel, you are never really off the clock, always observing the world and people around you. A total stranger on the subway can be ascribed a personality before the next stop. Or you may come across an intriguing comment from wherever. Write it down. You might be surprised when later it very neatly fits into a dialogue you are writing.
A good writer must also have self-confidence. By this I do not only mean the confidence it takes to face the keyboard, but also the confidence it takes when asked what it is you do to forthrightly reply that you are a writer. Most writers do not get famous or rich. So what? If they are honest with themselves, they will say that they write to write. There are distractions, there is stress in our lives. But all that evaporates when you are writing. It does for me. So, if you want to succeed at writing, then you must have discipline, clarity, perception and self-confidence. There are other qualities one could mention, but I believe the point is made.