The basics are surprise/rarity, emotional impact/narrative (which can include comedy, tragedy, drama, etc), geometry and composition (which can include focus control, depth of field, and motion effects), and controlled colour.
Colour control is the one a lot of people miss. The aim is to have a limited colour palette - either one dominant colour, or two or three punchy related colours (complementary or contrasting on the colour wheel) against a more neutral background (white/black/grey/less often - brown.)
Too many colours are chaotic. There are exceptions which can make chaotic colour work as a feature, but if you just snap a random crowd you'll usually get a photo that lacks something, and you're not sure what.
Newspaper photo pages are good for examples. Random sample:
https://www.theguardian.com/news/gallery/2020/jul/14/sammy-t...
You can see how few colours most of these photos have and how often there's a strong colour contrast. A "newsy" photo of flooded buildings still has controlled colour - base of green contrasting with blue in the foreground, and further bright purple/pink contrasts in the background.
And the photo of the soldiers with masks balances black/white against the pale blue of the masks, with complementary gold highlights.
Even the prisoner photo only has three colours - green on the prison shirt, pale yellow gold on the uniform patches and buildings, and some splashes of red, which contrasts with the green.
The opera audience photo is the weakest with a pale nondescript yellow/green wash against grey/white, but it (almost) makes up for it with very strong geometric composition in the architecture.
Edit: non-representational photos usually follow the same rules. The one big exception is high end art photography which uses a couple of specialised standard palettes (usually warm on the flesh tones) and a small selection of standardised subjects that signify "art" in that market.