Where I ride depends upon how wide the lane is. If its substandand meaning there is not enough room for a car to safely pass me in the lane (and that's mostly the case around here), then I ride the in right hand tire track essentially taking the lane. This forces cars to at least go partially into the other lane to pass me and keeps them from squeezing me off the road.
Of course, they occassionally still try to illegally pass when another car is coming over the hill or around the curve. The advantage is that I can usually hear the car that they cannot see. Being further into the lane gives me some maneuvering room when the passer suddenly decides he'd rather hit me than the oncoming car.
If the lane is wide enough, then I'll ride closer to the white line unless there is some type of hazard like a curb.
Dave