Mending is such a fundamental part of accomplishing an excellent dead drift that we have actually published about sometimes here on the Orvis News Fly Fishing blog site. (See here and here, for example.) Among the tough features of repairing is moving the line after it has actually arrived on the water, specifically if you have an old or roughed-up fly line since these will end up being hydrophilic–” sticking” to the water.
To prevent this, sometimes, you can really make the repair in the air, before the fly touches down. In this excellent video, Pete Kutzer of the Orvis Fly Fishing Schools, shows an interesting strategy in which drawing a letter C or D in the air with the rod suggestion will produce a heal.