The City Overview from the FOE Helper is a quick and useful way to show outlines and types of buildings in your city.
The City Planner Tool from FOE Helper is also quite neat:
https://foe-rechner.de/citymap/overview
You can directly import city data using FOE Helper tool in game. To use the tool on the website you need to make an account.
It'll ask for FOE Helper Player ID: (FOE Helper Panel) Settings > Version. Then to import (FOE Helper Panel): City Overview > Show submit box > Submit
On the website, login and choose which world: Tools > Cityplanner > New City > with my citydata.
It'll show movable grids. We can rearrange, shuffle etc. We can also save the city plan(s).
There is one other City Planner app, and it used to import your current city correctly so you could play with the design, but INNO BROKE THIS PART, STOPPED WORKING IN EARLY 2020 FOR CITY IMPORTS. You can still recreate your game city or design a city from scratch and try different layouts; move things around until you come up with a good plan or blueprint for how to layout your city.
http://foemanager.com/city-planner/
Once you come up with a plan, you have to make the final changes to your game city yourself, but this app allows you to play around with a copy of it before you wreck your live city. You have to register with an email address, but there is no confirmation process, and that also becomes your login for the site.
Your goal should be to connect everything to Town Hall using the least roads possible. Wasted space with roads is the most common city design flaw. No building needs more than one road connection, and if a building touches 2 pieces of road or roads on more than one side, that's an inefficient design. Also avoid putting roads around the edges of your city, if you can't use both sides of the road, that's a waste of roads. Don't think about it like a real city with roads going all around buildings and criss-crossing the city for traffic flow. Let there be traffic jams with only one way to get there, LOL!
From Progressive Era onward, some buildings require 2-lane roads. At this point you will need a major city redesign, but the same principle applies: you want to connect the most buildings with the least roads possible. Setup your 2-lane roads in the middle of your city so that you can use both sides of the road for buildings that require 2-lane connections. Branch your single lane roads off from the 2-lane road; only the 2-lane road needs to connect to Town Hall, and single lane roads can connect to the 2-lane roads, but it can not work the other way around (not allowed to connect Town Hall via a single lane road and later connect 2-lane onto those.)
It's best to move all your GB's, large buildings, and anything that only needs single lane roads to the edges of the city; this saves space as you use less road running out to the corners of your city if 5x5 and 6x6 chunks of land on the edges are all occupied by large buildings. Think of it like making a down-town area with your 2-lane roads in the middle, and a suburbs area with the single lane roads on the sides.
You should avoid 1x1 decorations or any decorations in general; the Aid button polishes everything in your city first and each deco wastes 1 visit from somebody - you may be missing out on motivations to your houses and supplies because there is too much to polish. These days, you should be solving happiness problems with Event buildings like the Grilling Grove, Jester's Stage, and many others which provide a lot of happiness.
If you have 1x1 spaces (like at the end of roads) its better to fill in with Celtic trees, neo sentinels, watchfires, ritual flames, all of which are more helpful than decorations and mostly don't need polishing/motivating.
Always use the best house you can, the 8 hour or 24 hour houses in each age are the best deal. When you get the 24 hour houses unlocked (starts in Colonial) you'll want to upgrade all your houses to those and you should then need less houses to get the same or better population. The less space you use on houses for population, the more space you have for troops and goods. Population demands are mostly cured now by Event buildings - be on the lookout for Celtic Tavern, Urban Metro, Orachard of Orange Dreams, and other Event buildings which provide high population.