I find a fly that really stands out does the trick.
For example on the harrison, while the fry are hatching I will run my flash fly and strip in fast using a clear sink tip. I generally do very well.
You can combine this with a bunch of different things. Some days even while they are surfacing it helps to either dead drift your fly down deep or let it sink for 30 seconds then strip in fast.
Another thing I do is run a BIG minnow. Same colours as the ones around, just 5X bigger or so. When I'm doing this I use this guy:
When I'm running a normal sized minnow to match the hatch I go with these guys.... Only when they are being really picky and mostly in "the lake"
If none of that works... I'll start switching up flies... Mickey finns, The C&R a fly I created while fooling around (pic to follow), crayfish patterns, and flashy olive woolly buggers. I always tend to start with the C&R as it has done well for me on all the rivers I fish... must be a decent minnow or something along the likes.
Cheers,
Dan