ADD MORE DESCRIPTION TO:

• Things most of your audience will never experience
• The small details that help make large emotions
• The biology and culture of aliens and magical creatures (though this might just be my personal taste, I have seen it asked about extensively in every author Q and A involving an author that writes about aliens or fantasy creatures.)
• The tiny gestures that make relationships what they are. This is not limited to romantic relationships
• Events that you want your readers to perceive as taking a long time

DO NOT ADD MORE DESCRIPTION TO:

• The setting (unless you forgot to put a decent one there in the first place. Most authors err in the direction of too much description, though, so it’s better to not add words if you don’t have to.)
• The exact nuances of every character’s eyeballs
• Concepts that most readers will already know about. There’s no reason to describe what a plague is or how to play Scrabble
• Drawn-out negative emotions. Though realistic, they can be tiresome to read about
• Things that happen within seconds of each other – the extra words feel like extra time