Much can be determined by practicing observational urbanism. Parts of my neighborhood in the Buckhead section of Atlanta were built prior to World War II and parts after the war. With my non-planner background even I can determine which parts of the neighborhood work well from an urbanist perspective, and which don't work quite as well. The area built prior to the war has sidewalks, short setbacks, narrow lots, few garages and a close proximity to the commercial areas on Peachtree and Piedmont. The parts of the neighborhood built after World War II have no sidewalks, much deeper setbacks with wider lots, primarily one-car garages and are more difficult to walk (although the neighborhood is still very walkable by Atlanta standards, and I live in the "newer" area).
There are cues and patterns in all areas for what works now and has worked well and what has not. We don't have to reinvent the wheel or copy blindly from other areas to make urbanism that works everywhere.