ALWAYS against oncoming traffic. For most of us that means on the left side of the road, as we are walking.
This is sometimes mildly confusing and amusing to our British Commonwealth and former Commonwealth friends, as it is contrary to their traffic pattern.
Walking against the flow of traffic, so oncoming traffic sees the FRONT of you as you are walking, gives the driver the best view of you, AND gives you a view of the oncoming vehicle(s).
Were you to walk WITH the flow of traffic, with the oncoming vehicles approaching you from behind, you would lack that instant of view where you could leap out of the path of a dangerously close vehicle. Conceptually, this is very similar to bicycles silent sneaking up on you while on a remote Camino trail, without warning you they are coming...
I also recommend that everyone either wear a safety vest (neon-yellow), OR similarly very bright and contrasting color so you attract attention from oncoming drivers. BE SEEN!
Hope this helps.