For me, my approach depends on several factors including the shape of the river, amount of bank available, bushes/trees, boulders, and what type of gear I'm using. Some places it is more conducive to get well above the run/stretch I think the fish are, out of their sight, then work down through the fishy lies. Others, I need to work from behind, out of their vision, then upward. I usually go with what seems easiest that still allows for success, and in some cases, I don't care because it probably doesn't make much difference.
But like SteelmonKiller20, on the Clack I am usually working from top to bottom. There is a spot on the Wilson that is easiest for me to work top to bottom, but in order to get there, I have to crawl along the bank because I can't get behind the trees and the water is skinny. Another spot on the Wilson, I have to work bottom and up because the fish lies are right on the bank and I can't get by them without a spook risk.