On rivers, here in the West, I choose my flies for smallies depending on the time of day and weather usually.........
Early morning..............it's almost, always, woolly buggers in black, dark brown and dark gray.
Mid day.......... it's always bright colors, i.e. yellow, yellow/red, red, orange and yellow/orange combos.
Evening, to me, is "magic time" when I switch to poppers, either cork, deer hair, or foam and all in bright colors for the "leg feathers",
red, yellow, orange and white. Same colors, matching or in a combo of colors, with the "leg feathers" and the popper itself.
If it's less than perfect weather.........cloudy, raining, threatening to rain, etc. I'll fish woolly buggers all day long, from early morning to nighttime.
"How to fish" these poppers and buggers I use the Bob Clouser instructed methods. If you'd like a really good idea, about how he does this, visit midcurrent.com and click on the link-"techniques" then scroll down to "Fishing for Smallmouth". it's a very informative article!
Good luck!