Well Best Kog,

at the beginning I would ask myself some questions:

- Is the city of great national or even international importance?
- Is it a large city or a small city, how many inhabitants?
- Is it a large River?
- Is this river shippable and if so, is my city a city with a large port?
- How much space is between the river and the mountains?

Old European medieval cities, even big cities, were only big in the very rare cases and an area of 1000x1000 meters was basically a big and important city.

So I would suggest to answer these questions, keep this facts in mind (without beeing restricted too much by them of cause )

Then I would start with the port, the nearby market place (f.e. 50x50 meters), than adding a church or cathedral, depending on the plannend amount of inhabitants.
After this you can create the mayor streets, crossing the city, adding some secondary streets and adding some residential houses and additional administrative buildings and warehouses and so on.
Even think about a city wall, or some watchtowers or both, maybe a castle or something... Just start and try to grow the city like it would have grown in it´s history