One of my favorite times to target smallies is after good rain has fallen in your smallmouth catchment and the velocity of the flow rates has increased, especially in spring and early summer. This is a time when I like to focus my attention to pool heads and rapids in particular.
With the increased flow velocity the riverbed is disturbed, causing aquatic invertebrates, crabs and fry to be flushed downstream. Big smallies will now pile into feeding positions in concentrated areas and I have had exceptional action during such conditions. I have also experienced how the action dramatically decreases after the water drops following high water velocity.
A good spot to focus on would be current seams right at the head of the pool. Also look out for large rocks that break the current right in the rapid as the bigger fish will often be hanging out here. For me, there are few things as exhilarating as hooking a bus of a smallie high up in a rapid and watching it launch out the water as it heads upstream!