There's good advice on here already, but a few quick tips...
Dominant fish tend to occupy a lot of prime feeding spots. So, that means a few things. First, larger predators are going to take their pick of prime positions that suit them best. If you're fishing grass lines, expect pike and musky to be a part of the equation because those are areas they tend to dominate. Similarly, if we were talking about a lake with a large, healthy largemouth population, they would also dominate a lot of similar habitats. Second, dominant fish within a species are going to get the best pick of spots available and advantageous to that species. You see it in underwater footage of trophy largemouth, in that they tend to dominate the best ambush positions in their area in largemouth dominant bodies of water. Now, applying the same idea to river fishing, you'll find the largest smallmouth typically at the tops and bottoms of a lot of riffles/rapids, boulder fields, areas of converging current with deep water access and behind the points on inside bends, especially if there's cover like downed trees or a change in bottom composition. These areas allow fish to get big without burning calories fighting current and once they get into the 3lb plus range, there aren't many predators that are going to push them from their spots. Big rocks often yield big smallmouth, not necessarily because they're the best feeding area, but often because smallmouth have been relegated to them and they can thrive there.
@smalljaw67 hit the nail on the head regarding bait size. Which baits depend on conditions, forage, and where you're finding fish, but big tubes, craw jigs, 4"+ swim baits, and anything representing the larger size of crayfish, gobies, sculpins, mad toms, hellgrammites, etc that smallies gorge themselves on can be really productive. I've caught smallies in the 16-19" range walking full sized Spooks. A similar common mistake is the idea that finesse fishing always requires small baits. This isn't necessarily true. If you can fish larger soft plastics T-rigged, drop shot, or on an appropriate jig head slow to the point of near agony, you'll surprise yourself with the results. Guys like Jeff Little are river smallmouth savants and boat lots of 17"+ fish dead sticking.
Anoter tip on the opposite end of the spectrum, has to do with how you fish your crankbaits in current. Fish will orient into the current nearly 100% of the time. One of the few situations fish will haul ass down current is if they're being chased. One of the best ways to simulate this is casting straight up current and ripping a crankbait down current through a boulder field. A good abrasion resistant line is important, and not a gauruntee, but this is a great technique for getting reaction strikes in current.
Hopefully this gives you some ideas to play with.