All the mechanics of writing are part of the craft. This is the stuff you can learn to make it so all readers can understand your writing and so your style contributes to the overall experience of your story. This might be the stuff that editors take care of, but editors are not responsible for all of it. Writers are.
Vocab & Diction or Word Choice
Reading a lot of stories and nonfiction content can help improve your vocab and spelling. If you have a real problem with basic words, search online for spelling games or quizzes to take, or peruse a dictionary or "Word of the Day" sites. Understanding prefixes, suffixes, and root words can also help construct words more easily. Writing is not about using the fanciest word, but if you do pull one out, you need to spell it correctly. Spell check can only go so far.
Basic understanding of parts of speech and word usage rules. This also extends to things like past, present, and future tense verbs, adjectives and adverbs and when to use them, and proper capitalization. Punctuation can change the entire meaning of a sentence. The Oxford comma is famously used as an example in phrases like, "We invited the strippers, JFK and Stalin" vs. "We invited the strippers, JFK, and Stalin." The first sentence means that JFK and Stalin are the strippers. The second sentence means that the strippers, JFK, and Stalin are three separate entities that were invited.
These are the fancy things like metaphors and alliteration that can either make your fiction writing unique and expressive, or bogged down in so much purple prose that your reader may be compelled to stare at a blank wall for an hour or two after reading to give their mind enough time to clear out from all the mess.
There are reasons to use a lot of these things in the story, but, in my opinion, it can be difficult to teach where it should happen and where it should not. Some things like alliteration (Starting many words in a sentence with the same letter sound) or onomatopoeia (Writing out sound words like boom and pop) align more with a whimsical or lighthearted subject matter. Others like foreshadowing, literary irony, and metaphor are frequently used in many different types of stories.
Metaphor + Simile
Foreshadowing + Flashback
Deus Ex Machina
http://literary-devices.com/ covers pretty much everything and gives examples.