In my opinion, the most important thing to remember while river fishing is not to spook the water that you're about to fish. I've seen entirely too many anglers do this very thing. They're standing in the very water they probably should have fished first.
The first tip is: When river fishing, remember to work the area that you want to fish in "sections". Don't just jump in and start fishing in the spot that you think looks the best or just fish the water directly below where you're wading.