Scout all the way down to the bottom of a major rapid. Sometimes, looking back upstream is the only way to spot strainers and submerged boulders or logs that may have an impact on your route. Lastly, look downstream from the top of the drop to retain fresh memory of your entrance landmarks. Find rivers within the river. Any stream is a braid of jets, chutes, eddy fences, recirculating hydraulics and rebounding forces.
Some currents dive under sheets of foam, then reappear.
Think of the array of forces as the elements of a cocktail. The raft captain is the bartender. Everybody aboard has to drink the result. Don't push it. Most often, float your boat at the speed of current, or even slower.