One thing I can definitely recommend is to create a fairly lengthy random list of names. In the past, when I ran city adventures, the PCs would inevitably do something unusual and get off the beaten track. Since I always struggled to find good names, especially when put on the spot, I found it handy to create a list of random names that you can stock in your local tavern, common room of an inn, barber shop (yes, I did have PCs that wanted a shave and a haircut once…), or just some name for local constables on patrol. Rather than just name the patron, "oh, his name is, ummm, Bob...and the girl is, uhhh... Mary." you can have a handy list to check off a name. "Oh yes, his name is Prentice Vellanas, and the young lady with him is Korinna Hightower..." I would have a column for human male, human female and any applicable demi-humans. Try creating a couple of good elven names on the fly and make it sound smooth and seamless in game? Not easy.
Similarly, names for taverns, inns and a few common shops (blacksmith, supplies, etc)
I agree with the above poster – the city should have a set of laws that they follow. If they are strict and lawful, PCs might need a reason to be out on the street after sunset, and guard patrols will be several men that are well armed and well prepared. If the city is not so strict, the guard patrols will be less frequent. We had one PC that displayed public drunkenness and was thrown in jail for a week! However, it was a very strict lawful good town that also frowned on drinking.
Landmarks are a good idea, too. The main town square, the market district, the castle, where the town watch is headquartered.