Any advice for building a huge city in minecraft?

I always pick a style of building first, then plan out key locations such as hotels, restaurants, shops, etc. After that come the roads, sewers, utilities, etc. This is followed by sectioning the city into industrial, residential, and commercial districts (there will be overlap, such as a carpenter shop in the residential area). After that, I fill I buildings following the period style that I chose (imperial, colonial, modern, near future, far future, SciFi, etc).

Some of these steps overlap, for example: I've been working on a medieval city for a while, and when I was working on the pub/hotel near the slums (poorer area), I was also building the road on that block as well as the sewer system.

I typically limit the area I work on at a time, and go block (distance, not thing) by block building.

Start by building roads and leaving squares of grass in between them. This will give you an idea of how large your want the city to be, and how much space you want the buildings to take up. Then it's just a matter of what kind of city you want (futuristic, medieval, modern, 50's style retro, etc) and building to that motif. You can just build a mess of sky scrapers if you want.

1. Watch videos of people building and get inspiration.
2. Listen to music while you build and be creative.
3. Have your friends help you build.

Download a few maps that other people have created and take a look to see how they do it, what blocks they use and what scale they use.