The subject is unclear or crowded
Image models handle one clear subject well and five competing ones badly. Lead with the main subject and what it's doing.
“A golden retriever puppy asleep on a red wool blanket” beats “a cozy scene with a dog, a blanket, a fireplace, a cat and some books”.
You didn't pick a style
With no style, you get the model's house look. Name it: “flat vector illustration”, “35mm film photo”, “watercolor”, “3D clay render”, “isometric”.
Lighting and camera are left to chance
Lighting sets the mood: “soft morning window light”, “golden hour”, “studio softbox”. Camera sets the framing: “close-up”, “overhead flat lay”, “wide shot from low angle”.
These two details change an image more than almost anything else.
The shape is wrong
A square image won't make a good phone wallpaper or YouTube thumbnail. Ask for the aspect ratio you need: 16:9 for landscape, 9:16 for stories, 1:1 for posts.
Text in the image comes out garbled
Newer models write text much better, but long text still breaks. Keep it short, put the exact words in quotes, and say where it goes: “the word “OPEN” in bold white letters on the door sign”.
Fix one thing at a time
When the image is close, don't rewrite the whole prompt. Change one thing (“same image, but at night”) so you can see what each change does.