I love fishing for Smallmouths! They're my favorite freshwater fish!
I've done well on a lot of different flies. For me, my primary "go to" flies depends on where I'm fishing, as I've fished some tiny streams & some large rivers for them, so I choose different types of flies for different water.
In smaller streams, I'll use a large stonefly nymph that I've done well with, a Clouser style leech pattern, or on the surface, foam bodied flies such as Triple Deckers, or Chernobyl Ants. The stonefly nymph is tied in size 2, and the pattern recipe is on my blog, the others are tied from size 6 to 2. I usually tie the stonefly nymph in black, or olive variations, but have tied it in other colors. The Clouser style leech is tied with Ostrich herl & some flash, very full, and usually in black. The flash I add is usually Flashabou or similar, in copper, bronze, and or black. ( I often mix the flash.) I may add some electric blue too sometimes, but only a couple of strands.
The foam flies are tied in hopper colors,(tans, browns, greens) white or black.
In larger waters, I'll use the above flies, but more on the larger size, plus Clouser Minnows, primarily in baitfish colors like olive & white, gray & white, black & white, plus chartreuse & white. I use Deceivers quite a bit too & in the same colors, and both of these in sizes from 4 up to 2/0 & 4-5" long. Smallmouths will eat the big flies!
Another pattern I really like is the Murdich Minnow, and in particular a variation that Joe Cornwall ties.(The pattern is described on the Fly Fish Ohio, Fly Fishing and Fly Tying Multimedia Magazine
website. There's some other good patterns there as well!) Here's the direct link to the Murdich Minnow article: http://flyfishohio.com/Murdich_Minnow.htm
I also like a Sneaky Pete variation, and I make them in 3 colors, chartreuse, white & black. Except, I prefer splayed neck hackle tails on mine with some added flash, and all will have a black collar. I make them big too, from size 4 up to 2/0. I use straight shank worm hooks on a lot of my flies for bass!