The idea of touching as many squares on a grid as possible works well with a road atlas. I can easily flip through and see which pages my rides have spilled onto. I like it, but so far haven’t made that a personal priority though.
Here’s another one: Try to “capture territory” by completely encircling areas on the map and connecting them to the main body of routes.
Like others have said, it’s getting hard to find any unridden roads locally. I have to drive an hour to a start location if I want to ride something fresh. Worth it though.