One of the keys to great fly casting is developing the ability to feel weight transfer. Your line is, of course, weighted, and you must be able to sense exactly when the rod loads.
Granted, that “weight” looks like a 90-foot-long piece of spaghetti. But unlike conventional fishing, in which the weight is concentrated in the lure (or the bait) and the line itself is virtually weightless, in fly fishing, the flies weigh very little, and the line itself contains the mass. That’s key, because you need to be in the mindset that the long fly rod you are using (and they make the average fly rod 9 feet long for a reason) is a launcher, specifically designed to help you throw that weighted line.
But you need to be thinking about your fly line as much, or more than, you think about the fly rod itself during the course of the cast. One of the best practice tips is to try and “cast” the fly line using only your hand. Done right, you can feel that weight extend behind you, and that sudden tunk will tell you when to transfer the energy and move the cast forward. Some expert casters can actually throw more than half a fly line without a rod at all. When you add the fly rod to the mix, casting naturally gets a whole lot easier. But it starts with feeling that weight transfer in your bare hand. A great rod will help you do that, but there is no substitute for practice.