A few things that make submissions stand out in the archive.
Hide the UI
Turn off the HUD — F9 or F11 in most Anno builds — or use the new Photo Mode, so nothing but the city shows.
Turn off Photo Mode's blur
Photo Mode's depth-of-field effect softens the edges of the frame for atmosphere, but it also softens the build — turn it off so the whole shot stays sharp and other builders can actually see what you made.
Find the angle
A slightly elevated three-quarter view usually reads better than a straight overhead or a dead-on street level.
Show more than one spot
Include a few different corners of the build — a wide shot plus the details you're proudest of — not just a single photo.
Write a real headline and description
A specific title and two sentences on what you were going for tells the story a screenshot alone can't.
List your mods
If mods shaped the look, add them in the Mods field — it's how other builders find out what's possible.