Here's some things to keep in mind.
0: Do not sweat
while writing. Write your post. When you're finished,
then start editing.
1. Figure out your bad habits and try to reduce them. One common issue are words you overuse. "Just" is one of my bad habits. "As" ("x happens as y happens") is a common one I see.
2. One trick you can do to simply make your writing
look nicer is to vary the size of sentences and paragraphs. Sentences all the same length, paragraphs all the same length, make the eye glaze over in disinterest. Change it up.
3. Avoid cliches like the plague.
4. You mentioned repeating things. One of my personal annoyances is the specific phrase "When YC does x, MC..." So I would say avoid that.
5. Try to avoid starting too many sentences in a row the same way. Too many "The", too many "Character name".
This is hard in English, since nouns typically come first. It can take a little nudging. Sometimes it's unavoidable or doing it will make the sentences to avoid.
6. EXPERIMENT. Try new things. Someone earlier mentiond "voice". A character can have a particular voice, or an RP can have a certain tone, that spices your RP up. Like say, everything is grim and gritty and dark. Writing from one character's perspective can also sound different from another, their attitude or behavior bleeding into the prose about them.
Finally, a suggestion when it comes to the actual content:
7. Focus on how your character
feels. Emotion is a pretty big part of what we're doing here. The what, the
why, and the how that looks. So when your character is upset and mad, she glared through the sting of unshed tears.