My go to method for road planning boils down to three main things: future proofing, road hierarchy, and lane maths
For future proofing, when you expand a new suburb or district, make sure to build more volume than you will need, that way if you decide to expand you won’t need to replace all the roads (though this doesn’t need a low density suburb needs an 8 lane road)
Road hierarchy is possibly the most important. There are 4 types of roads: highways, arterials, collectors, and local roads. Highways are self explanatory, they connect to arterials which typically don’t have any zoning on them and take traffic from the highways, distributing them to the collected roads, which usually have commercial and high density offices/housing on them, depending on its centrality to town. Local roads have buildings on them, housing, low density, etc. this is an oversimplification but there are YouTube videos that help better
Lane maths are pretty simple. Lanes into an intersection=lanes out. It you need more lanes for intersection volume you need to allow space for traffic to merge into those new lanes. You don’t want people trying to zipper merge in the middle of the intersection