While you may not always be able to see fish, you can learn to "read" any river, as they all share common traits. Learning to read a river means being able to recognize the type of stream habitat the fish are most likely to favor at different times during the day, both at rest and while actively feeding.
All streams or rivers have the same basic sections and share common traits. Fast water can be broken down into rapids, riffles, and pocket water. Slow water can be broken down into pools, slicks, and eddies. Fish prefer to live in a slower current most of the time as this helps them conserve valuable energy. Trout generally lay up in front of or behind rocks or in the gentle seam of where two currents meet.
THE FEATURES THAT WILL CREATE SLOWER WATER IDEAL FOR ATTRACTING AND HOLDING FISH ARE:
Boulders: Fish love boulders for the protection and feeding opportunities they provide. Boulders protruding from the water's surface create a pocket of slower water. The front pocket is formed by the damming effect on the current, causing the water to stack up and create a bulge of slower water. You will recognize this bulge and sometimes see a wave breaking just in front of it.
Stream Banks: First look for fish along the shore or banks of the river where the water is deep enough to hold fish or allow them to move into the shallows to feed. Particularly in the early morning, trout will move into surprisingly shallow "skinny water" to feed on nymphs or emerging insects. Look for active fish down stream from any irregular shoreline feature, bump or other protrusion you can see, such as a series of rocks jutting into water. Fish will hold in the slack current behind obstructions like these, so you can be confident they are there whether or not you see them feeding.
Fallen, Submerged Trees: Finding fish means first finding their habitat, and trees that have fallen or been swept into the river provide plenty of that. Whether still attached by roots or lodged against the bank or other structure, whole or partially submerged trees create a slack current attractive to fish (look for a slick water area or area of calmer water).
And check out this video... it's a pretty good overview.