Smallmouths are my favorite freshwater fish species.
There's been some awesome suggestions for fly patterns made here. One note, SM bass will take flies that are quite large. Over the years I've read many times that you need to down size for them compared to LM bass. Although this may be true in some places, I've yet to find it to be true generally speaking. SM will eat a lot of the same things that LM bass will eat.
I once hooked a SM in the MD portion of the Susquahanna River below Conowingo Dam on a 8" saltwater style pencil popper while fishing for Striped Bass. That SM was only about 6" long. I've also read far too many accounts of monster SM's being caught by anglers chasing Muskies & Pike, and caught on the lures used for those species. Don't make the mistake of thinking that only small flies need to be used for SM's.
IMO, anything that is commonly used for LM bass will also work for SM bass. The primary difference is how you go about fishing for them. SM generally are more susceptible to faster moving flies, while LM like things slower. Not always true for either, so you need to try different retrieves to see what they want.
There are a lot of fly patterns commonly used in saltwater that can be very productive for both too. I've caught many of each on Seaducers & Lefty's Deceivers, as well as large Clouser Minnows & Half & Half's. One of my favorite "crayfish" flies is a Squimp, which is a Bonefish type fly. I simply tie them in colors that better match local crayfish. Many of the "flats" flies used for Bonefish, Permit or Redfish can be good for SM's & LM's.
There are also quite a few flies that the Steelhead & Salmon folks frequently use, that are superb SM bass flies as well. Flies such as Intruders, MOAL,s & even Bombers are attractive to SM's.
Here in MD we have many small streams that hold SM's including many of our trout streams. Depending on the stream, or river I'm fishing, I've fished for them using everything from a 3 wt to an 8 wt, but have most often used my 6 wt.
In river & stream environments, they'll be found in most places that trout might be found, except the bass tolerate warmer water than trout. I've read that SM's don't relate to wood very well, and will be found instead where there is rock or gravel. In some streams & rivers here, I've caught them many times in deeper holes where there is large undercut root mats or sunken wood. IMO, with a lack of rock, they'll still seek whatever cover or structure is available.
Here's some flies I've used for SM's.
