First off I want to say that fly casting is not difficult, it does however require different arm motions than other types of fishing. Learning to cast is often compared to learning a golf swing – almost any golfer can teach you to swing a club, and you will almost certainly get hours of enjoyment chasing a ball round a course, but it's no substitute for an hour or so with a qualified professional.
Spend one hour in the company of a good instructor and you will learn the basics of fly casting. Learning to cast properly early on will save you heaps of frustration and should keep you from developing the bad habits that often occur when beginners try to re-invent the wheel. Fly casting is the foundation of the building block that gets you along the road to becoming a successful fly fisherman, whether you want to fish in streams or in rivers.
Fly casting is done usually by throwing the line back and forth in the air in what is usually called a front cast and a back cast before the fly is allowed to land on the water and it's this that is usually what gives the beginner problems. To master this relatively simple skill you need to master a few fundamental rules such as achieving good timing.
If you manage to satisfy the physics related to the methods you are being taught, and thankfully the physics are simplified by observing a few basic rules, you will overcome any initial difficulties you meet. These are the rules of substance, because they are laws of physics and natural forces such as gravity. Fly casting is all about adaptability, you have to learn how to load and unload the rod in a correct way. As long as the rod loads correctly, you can cast almost anyway you like!
Fly casting is a very different to spin casting, with a fly rod you always cast your line, not your lure. It is as much an art as a science, much like a perfecting a graceful golf swing or performing a perfect turn on skis. If you develop bad habits at the beginning, overcoming them can be difficult, but if you understand the principles of efficient fly casting from the start learning to cast a fly will be easier.
Fly casting is not something you will easily learn from a textbook. You will need someone metaphorically holding your hand when you first start out. If you decide to trust me on just one thing, it's that time with a qualified professional instructor will be money well spent and will save you hours of agony later down the line.
Fly fishing can be whatever you decide to make it – so above everything else, make it fun!