While crayfish are the favorite and most universal food source, smallmouth will frequently feed on smaller fish such as sculpins, suckers and minnows. I find that these smaller fish will relate to wood structure very frequently. Root balls and fallen trees are stacked full of baitfish and therefore attrack smallmouth bass. Needless to say I am always on the lookout for structure under the water such as logs when looking for smallmouth bass. Even if the log sits on a sandy bottom smallmouth will still relate to it.
Because smallmouth are heterotrophic they don't like to expend unnecessary energy otherwise the must find more food. Smallmouth will take cover from the current behind and in front of boulders. Both sides of boulders have pockets of slower moving water and make perfect ambush points. Current seams where fast as slow water meet, eddies, and drop offs all provide smallmouth with a place to take rest from the current.
In the rivers in my backyard I find that almost every pool tailout has a deep spot or drop off where smallmouth congregate. My favorite tecnique is to swing a fly over the edge of the drop off. If the water is moving slower I will use the Tequeely otherwise a HiTail works well too.