Sometimes, it’s easier to build upon (or complement) an existing piece, rather than start fresh. It’s the difference between taking algebra for the first time and taking higher math after having mastered the skills of lower mathematics. https://sarahleastories.com/2018/04/29/poem-a-day-april-2018-writers-digest-challenge-29-theme-response-to-a-previous-poem-this-month/
If you need to strengthen your dialogue skills, write a one-act play; if you need to strengthen your description skills, write a letter.
One of the most prevalent inconsistencies I see in the longer works that come across my screen is shifting tenses, which can confuse your reader. This is why writing in the present tense is tricky (and why writing in the second-person present tense is even trickier). Be aware.
Except for romance, the only reason a character needs a physical description is if it pertains to the story. Of course, this is a so-called rule I break all the time. Just don’t try to force your reader to see exactly what you see by over describing them.
A twist ending must have subtle clues leading up to it. If not, then your denouement comes across as a cheap trick (as a deus ex machina ploy). Hint at things along the way; foreshadowing is great for this. It is a joy for someone to read your story a second (and hopefully, a third, fourth, etc.) time and find those clues like overlooked Easter eggs.
I almost always go over the word count. When that happens, the first thing I look to cut is backstory. You don’t need to mention more than once (at least in a short story) what someone looks like. For example, the story I’m writing now doesn’t mention the main character’s hair or eye color. Save that for romance novels (e.g., his luxurious blond mane, her luscious auburn locks, his mirthful baby blues, her luminous green orbs, etc.).
When writing about writing, avoid mentioning anything about light shining on shattered glass, never-worn baby shoes, and grandma-eating commas, as most writers already know all about these things. Don’t regurgitate.
Editing other people’s work will help you become a better writer. Seek out jobs that force you to pay close attention to detail. The mistakes you recognize in other people’s work, you will recognize in yours.
Write what you know first. You can fill in the details later. Construct your skeleton first, add what it holds in, and then what holds it all together.
I learned in a creative writing class (as well as a professional and technical writing course) how to draft a process analysis. I not only create an outline of my characters (including traits, quotes, etc.), settings (time and place, as well as historical events, slang, fashion, etc.), and plot (my subplots usually appear as I write) before I start writing, but I also create a process analysis, so I can build symbolism into my work. For example, I am writing a Southern American Gothic horror short story and created a list of all the different types of symbolism I wanted to include. This list helped me do that. https://blog.reedsy.com/literary-devices/