4. add descriptive layers
I think this'll answer your first question since this is how I think I show off my writing style. Add a couple of more words after (and maybe before) an action or thought. Like my example above, I could have just left it as "I bit my cheek as I thought "oh please, like how you didn't mess up your marriage?" But I'd get punished when we go back home"
It's simple, yes, but boring. Adding a couple of words help the immersion. Like in Killua's paragraph in his second pov of chapter 1 you
pointed out the eyes but didn't divulge deeper into the meaning other than the fact that they look like the night sky. You could have said:
"As the blue haired girl walked closer, I gotten a closer look at her eyes. Deep blue like the night sky and stars that were projected onto it. But that was the thing, the stars were projected. Like a facade that became real.
We stared at each other as our parents talked. The long I looked, the more tranced and uncomfortable I felt"
(Bonus points if you can showcase how Killua feels about eyes)
Side note: check your grammar. Some sentences are run on and could use a period or two. (Literally everyone has this problem so no biggy ^.^)
Sorry if this reply is long and maybe a bit critical, but I hope this helps!