I've been practicing at building planned cities so that one day I could get a city journal. I basically (badly) terraformed my terrain, planning where I want a bridge, a mountainous area, a quiet district, etc...
Then I built all the roads, using some interesting sights (Roundabouts, etc...).
Then I decided where I wanted the residential areas, and placed it. I made the commercial area by planning it to be around a main avenue to reduce traffic. Then I placed the industrial area a bit further in the map, and made a semi-long road going to the trash dump.
A railroad links the three areas I mentionned, although they also have road connections. I put bus stops BEFORE the citizens started building, else you find yourself constantly destroying homes.
Of course, I'm using ordinances to make this a painless process. I don't think I would be able to achieve a real city building (All planned in advance) without heavy use of cheats.
On the city I made without using Ordinance, you end up fighting pollution once you get your solar arrays, and the traffic is generally bad.
Including avenues generally mean mayhem if you didn't plan in advance where you wanted them.
I think the best planning would be a central avenue which leads to most of your districts - This way you reduce traffic a LOT.
