The key to any hook set and fight is making sure you are positioned properly. Before casting into a hole, take a moment to think about where the fish are and where you need to be when the fight begins. Ideally, you want to be downstream of the fish (they are usually facing upstream unless you’re fishing an eddy).
Because creating a proper hook set requires propelling the fly against the direction the fish is facing. If you are upstream of the fish, an attempt to set the hook will usually pull the fly right out of the fish’s mouth. Once the fish is hooked and the adrenaline-filled fight begins, try to stay downstream of the fish for the same reason.