I find this scenario extremely rare as in most cases I’m envisioning, there is a middle turn lane separating the two opposite lanes. Either from a light or just as a buffer between the flows of traffic.

This is all to say, there aren’t any hard and fast rules and there are too many scenarios to cover with a blanket statement like “The left lane is for passing. If you’re not passing somebody, move over to the right lane. It’s not that hard people” (comment above).

victorz said it more succinctly below.