When replacing your fly line it’s important to make sure the line is stretched properly. In the video below you’ll learn how to do this to get the most of a new fly line.
It’s as simple as connecting your new fly line to your old leader and tying that to a tree. Then all you have to do is take a walk. Once you’ve reached the end of the line, put your finger over the reel to prevent any more line from coming off and pull the line tight. It will stretch more than you think. Next, hold it for about 30 seconds.
This way the line is already stretched out for when you set the hook on that massive fish.
Source: NewFlyFisher