Most writers have a gift for some, or even several, aspects of the craft, but no one is a natural at the whole process.
1. Mechanics--grammar, syntax, punctuation, spelling, style, etc.
2. Non-fiction, fiction, poetry.
3. Non-fiction--topic, theme, essay, article, book.
4. Fiction--genre, plot, characters, dialog, setting, viewpoint, and theme.
5. Poetry--topic, structure, and passion.
The mechanics of writing consists of a knowledge of grammar, syntax, punctuation, spelling, and style. Although a writer may not be aware of grammar, he or she automatically makes use of it in order to be understood by the reader. The English language follows certain rules of words, their order, and their meaning if one is to comprehend the purpose of the writer. As well as syntax, in writing certain customs in the use of punctuation marks have been established and are acceptable by most writers and readers. Spelling has also been established by practices acceptable to authors and their readers. Then the manner in which the writer uses all these mechanics begets his or her style.
Now writing can be divided in three broad classes: non-fiction, fiction, and poetry which are sub-divided into still many more species. With this great variety, it becomes obvious that no writer is proficient at all these aspects of the craft. Some are adroit at writing non-fiction, be it reporting, informing, or persuading, while others are gifted in fiction, be it short stories or novels, while still others are endowed in poetry, be it haiku or epic.
Each class has its special characteristics: non-fiction requires a choice of purpose, a theme, a topic, and the abilities to put words, sentences, and paragraphs together to achieve that aim. Here again, some writers are better than others at this. Some write articles, others essays, and others books. Each aspect of the craft can be developed, but some have a natural affinity and aptness to a component of the business, yet none is adapt all details. One may be strong in description, another in narrative, or another in argument. A gifted writer usually excels in several aptitudes, but none are successful with all.
Similarly, in fiction, some authors excel at characterization, others plot is their forte, while still others outshine in style or artistry. If one looks at the great writers, one sees immediately that some excel at characterization. Characters that they created are remain in our minds and continue to be remembered from generation to generation. Charles Dickens characters are unforgettable. Others excel at plot; Jules Vernes plot are as realistic today as when he wrote them. Of course, there is the master of all, William Shakespeare, whose characters, plots, and artistry live on from age to age.
Poetry is a genre of it's own with axioms of its own. But here also, certain aspects of the craft are more developed in some poet than in others. Some concentrate on form, while other on content. Each poet perfects one or two aspects of the craft, but seldom all. Again Shakespeare comes to mind, but even he was not completely proficient entirely.
No writer is entirely excellent in every aspect of writing although every one would like to be. The best one can do is to develop those areas that interest them most.