What advice would you give to a person who is modeling a 3D city for playing on a mob. platforms?

Question

3D

The city can be quite large, about 3 km. 4 km, will be densely rebuilt with houses and other households. Yes, and the game is made on the engine (can not be) Unity! So, I remember either reading in the Unity documentation, or somewhere else, that it is not recommended to make long (stretched) triangles ... And I ask you to give such universal advice and also specific advice. Tips to help make models lighter, but still look reasonably acceptable or even pretty. So... speaking specifically, I will need very low-poly, but seemingly nice models: benches, poles, horizontal bars, flower beds, trees, borders, etc.
ps I myself also have some experience in this area, but I would like to learn the methods and techniques of those who have good experience in this

Answer 1

To make the city look beautiful and work smartly, you need to make LODs for each model. Here is a great tutorial on the topic.
And about stretched triangles - some garbage.