It depends in large part what your (work) situation is, where you get your spatial data and what control you have over those data, whether shapefiles, geodatabases, external services, etc.
Follow all file/folder naming rules. This link is a bit old but the rules still apply. https://community.esri.com/t5/data-management-blog/how-to-name-things-in-arcgis/ba-p/897194#U897194
Consider organizing data under your control thematically such as Access (roads, trails, RR), Hydrography (rivers, lakes), Administration, etc., and stash these feature classes in their unique geodatabases (or folder if shapefiles). They can be further organized within geodatabase feature datasets (not the purpose of a feature dataset but can be a useful organization tool). All feature classes in a feature dataset must be in the same coordinate system and will be forced as needed.
Take a few minutes to add and update basic metadata as needed.
Consider creating a structured group of layer files that you can easily add to Maps without having to search for their underlying data source each time. Be aware that when you open a Map in a Project a layer will (try to) display the current state of its data source.
Never assume that shapefile or geodatabase polygon or line/arc data that you download are free of geometry errors. I always run GP tool Repair Geometry on any data sources that I download even from “official sources”. Always.
