In parts one and two of this series, I focused on brainstorming some basic ideas about my city and some interesting locales the PC's might visit. I gave two examples in part two, but at minimum you want to have a couple of inns/taverns, an armor/weaponsmith, and a magical sundries shop. It wouldn't be a bad idea to flesh out how religions are dealt with in your city as well. Ask yourself, what are the dominant gods of this region? Do any of them conflict with one another? Where are the temples devoted to each god located within the city? Religious motivations can make for excellent adventure hooks within a city, so don't overlook them.
Of course, to bring any city to life you're going to need some interesting NPC's. Note that you don't really need to spend hours upon hours creating NPCs for your city. A lot of wasted time and effort can go into making up NPC descriptions for each and every citizen of your metropolis. Do you really need to spend 20 minutes writing out a long description of Nook the chimney sweep? No, you don't. It's a common misconception that in order to be prepared to DM, you have to have a grimoire full of detailed NPCs down to every small minutiae of detail. That simply isn't true. Sometimes you are allowed to wing it. That said, you will want to spend some amount of time focusing on fleshing out the major NPC's of your city, especially the ones your party is likely to run into.
In my example of Crestfall from part two, I have at least 3 important NPC's created simply from spending time developing a couple of locales, and defining some particulars about the city. We have Magrem, proprietor of Magrem's Marvels and Delights, Esmelra Ravenpeake, owner of The Harpy's Haven Inn/Bordello, and possible leader of the thieve's guild, and a yet to be named, former adventurer who is now the figurehead ruler of the city. Again, we don't have to spend a lot of time on each major NPC. Just a few minor details and notes will go a long way for you. In the examples I will use, all three of these NPCs are adventurers or former adventurers so there will be some notes on their stats included. Keep in mind, these really won't be necessary when creating 0 level NPC's.
Here are some basic examples of my brief NPC notes:
Magrem the mage (H male, MU L15, AC: 0, NG, INT 17, WIS 12, HP 35)
Description: Old man with a slight hunch in his back, thin and short graying beard, spectacles. Often found reading over some ancient text in his shop. Tends to be absent minded and dishevled, his mind easily wanders off to other topics. He is a friendly man, but is impatient with those that wish to dig around in his shop especially those who aren't magic users.
Esmelra Ravenpeake (H female, T L18, NE, THAC0 12, AC: -2, DEX 18, CHR 16, HP 54,)
Description: Beautiful woman in middle years with long, black hair past her shoulders and blue eyes. Very charming and flirty personality with patrons of her establishment, but also shrewd and cunning. She is the leader of the city's theives' guild, which meets below The Harpy's Haven Inn. She keeps a Dagger of Life Stealing on her person at all times.
Deardemont Ironhold (H male, F L12, CG, THAC0 9, AC: -3, STR 17, DEX 15, WIS 9, HP 65)
Description: Middle aged man. Slightly short in stature, with brown hair and goatee speckled with gray. He is ruler of the city of Crestfall, but only in name, although he isn't wise enough to understand this. He's rash and prone to ill judgment, but the city coucil keeps him under control. He spends most of his time focusing on stopping the thieves' guild within the city, however they always manage to lead him along on wild goose chases. This allows the council to focus on more important matters like running the city.
These are a few examples of how you'd describe the major players in your city. You'll see there isn't much there. Just a few notes on what they look like, some key stats, and a bit about their personality. It's not a bad idea to link them together in certain ways, such as Deardemont always chasing after the thieves' guild, which surely is a major point of frustration for Esmelra. Certain things you'll want to focus on when fleshing out your NPCs is deciding who is influential in the city, why they have the influence they have, and what possible implications this could have for the PCs. Once you start developing the NPC's along with the places you've created, things will begin to come together and adventure hooks will begin to reveal themselves.
As another tip, I'd recommend having a handy stock of NPC names available. Just a small piece of paper in your DM notebook with various insignificant names which you can quickly give to the random NPC's the players are sure to encounter in the city. If you find yourself stuck on NPC generation, have a look at Kellri's Classic Dungeon Designer Series #4 - Encounters Guide. On page 26 there you'll find quite a few handy tables which will help you randomly generate traits and descriptions for your NPCs. I highly recommend the guide in general as it contains a wealth of information any DM could use in his/her game.
In part four, I'll talk about some techniques to go about mapping out your city and keying it with special locations you've created.