Any good way to plan Ethernet runs in an older house?

I’d look for guides that show how to inspect a wall cavity, use a borescope, and work with fish rods, rather than expecting one video to cover every old house. Framing varies a lot. A cable stopping partway down can mean blocking or fireblocking, not just a snag, so don’t keep forcing it. Check the route for wiring and plumbing before drilling, and make a small, repairable access opening if you need to see what’s there.

For a first pass, I’d favor interior walls and routes beside a stairwell, closet, or other spot where a small access panel would be easy to patch. Fish rods can be easier to steer than a long flexible tape, especially when there’s insulation, but they won’t solve every blocked cavity. A camera scope can help show whether you’re facing insulation, a stud, or a horizontal obstruction. Test each run before closing anything up.

There may not be a clean hidden route for every cable, and that’s fine. Existing coax might support a network connection with suitable adapters, which can avoid opening walls. If a route through an attic or wall still looks difficult, a neat surface raceway or a carefully planned exterior route may be less disruptive. I’d avoid using heating, plumbing, or chimney spaces as cable paths, and don’t put ordinary cable in air-handling ducts. Check local requirements and cable ratings before considering any duct route.