River fishing is 80% about eliminating water that won't be holding any fish and spending your time fishing water that will. Generally, slower moving and deeper water is where you'll find most of the fish. Floating line with a weighted fly will cover many situations, but sinking line can be effective if you find deeper pools and back eddies. Expect more snags and lost flies with sinking line though. As a rule, avoid water with obvious current, and look for slack water behind sand bars, points, and bends. A black woolly bugger has outproduced any other fly for me in my river experience.