I was taught to always let it sit for a time before the retrieve, how long is up to you and the fish. The old Rapala method was to wait for the rings to disappear and then pop it 3 times, wait, 3 times, wait, repeat. Spring Smallies will wait long periods and then strike a still fly/lure, but I never have the patience to wait more than 5 minutes.

A hint for LM in still water. Cast to the farthest point from shore that has structure/cover first and work your way in. Say there is a drop-off 20' from shore, another at 15' , and then a tree laying down all the way to shore. My first cast will be over the first drop-off, the second cast at the second drop-off and then move in on the laydown 3' per cast until I hit the shore or even land the fly and hop it back into the water. Remember that the fish will be looking into deeper water and if the first cast is over him, he is likely to spook.