Dialogue and how to include foreshadowing without being too obvious.
Also I struggle how to explain stuff without making it an info dump. I take the advice of a post I saw once which said to act like your readers are already familiar with the world and characters to avoid info dumping. Of course the post was about fanfic but it was mentioned cuz since it’s fanfic you can skip introducing the characters in great detail.
Like you don’t even learn the last names of my characters until chapter 3. Honestly you don’t even know the name of the cat familiar (or even that he is a familiar) until later. I think I’m working that into chapter 4.
As far as dialogue goes I suppose I have the benefit of being born and raised in Texas and I’ve just decided that my stories are all set in Texas unless otherwise stated... so I’ve got a lot of slang I can utilize.
Anyway so it’s mostly the writing part I struggle with. The art, I usually struggle with props or detailed rooms or things like trains / cars / etc. Which sucks. Also perspective, particularly in the case of bedrooms. Mostly cuz I draw traditionally so I can’t zoom in to get all the details and still get the perspective right. But I try to figure it out somehow.