hi Innes
I'd second all the suggestions thus far. You've clearly got reservoir experience, and I'm guessing some salmon experience (?) so it's about learning river trout craft i guess.
For the rivers, if you're interested in catching trouts on dries, I'd suggest fishing less, casting less, and watching & waiting more.
Get to a pool. sit down at the tail of the pool, looking upstream. Wait 10 mins before doing anything. Time it on your watch! 10 mins seems like a loooong time. Watch and listen. You'll see the patterns of water, you'll spot the changes that show rising trouts. Diving straight in, you will spook fish you didn't even know were there. If you see a rise on the far bank, sit tight. Wading across to that might disturb other trout in mid-stream.
Just walking up to a river and swinging flies will catch fish, but watching and waiting and picking your target can be more productive - after all, if a fish is rising and feeding, half the battle is won. You know where the trout, it is eating and looking for food. Put a fly in its path... Simple in theory, of course...