The fastest and most efficient way to learn a new sport such as fly casting is with the guidance of an experienced instructor. Ideally this experience includes understanding the various modalities of teaching and recognizing what methods work best for the student. For example, one student learns best through visualization, while another is an auditory learner. Other methods might include an instructor using a hands-on approach holding the fly rod with the student and mimicking a cast, or teaching through pantomime.
No doubt there are fly casters who improve through self-discovery but most only succeed in reinforcing bad techniques. In my experience the intermediate caster is often the most difficult to teach because the bad habits are ingrained with “muscle memory”. I prefer a beginner anytime.
While fly fishing guides do a commendable job putting anglers on fish, most lack a basic teachable knowledge of casting fundamentals. An ability to cast and guide does not always translate into an ability to teach. I tend to look at fly fishing guides and fly casting instructors as two different professions. Not competitors but experts that should complement each other with the shared goal of setting the stage for a more enjoyable fly fishing experience with their clients.
Personally I hope more fly fishing guides and others in the fly fishing industry become more interested in teaching the proper fundamentals and essentials of fly casting. Positive signs in this direction are becoming more common. I am aware of some fly shops in my area of Idaho and Montana requiring FFI (Fly Fishers International) casting certification for their guides.
I would encourage fly casters of all levels to seek out qualified instruction to improve their casting. The Fly Fishers International website provides a list of qualified instructors throughout the USA and worldwide who have undergone extensive training in teaching fly casting techniques.
FFI Master Certified Casting Instructor