Most mistakes are because of a misunderstanding of the overall principle: Waze is not a topographic map, but a navigation tool. Many starting editors try to make the map in Waze an exact copy of the actual situation. Roads are split; pedestrian boarding walks and cycle paths are added; perfect rounded corners and area places are exactly drawn. The actual goal of Waze is to get the best routing instructions. The less detail on the map, the easier and faster a map can be interpreted during driving, especially on small smartphone screens.
Another reason to keep the detail as low as possible is speed. The less details the less bandwidth the downloading of the map requires. Also the less junctions there are, the faster the route calculation is. The number of junctions that Waze can handle in one route is limited. So keeping the number of junctions as low as possible allows for a longer route.
To help you, Waze has created a number guidelines. That is what this page is about.