A good selection of flies can be critical to catching fish.
A common question for beginning anglers is how do I choose the right fly? Well, on the simplistic level you can look for bugs flying, in bushes or clinging to rocks in riffles. From there you can simple look in your box for fly that is a similar size, shape, and color. Being familiar with bug life on the river will really help you prepare for what you might need. Typically bugs will have a nymph or larval stage, an emerging stage, and an adult stage. Sometimes fish will key into a specific stage and species of bug particularly when there is a lot of bug activity. This can make finding the right fly a laborious game of switching flies and techniques until you can determine which fly the fish are keying in on.