[surfrod]

this comes up a lot and the best advice I can say is to get together with another experienced fly angler, or to Capt. Lou above (!!), and get some tips and help casting. In our area, while freshwater pond / lake fishing involves traditional casting, fishing on-stream involves a lot of hybrid casting: roll casts, sidearm casts, using the stream/river to load your rod to be able to present your fly to the pocket across and up from you, on and on. One day on stream with an experienced angler will give you the idea, and then it will be a whole lot easier for you to experiment on your own.

the best would be someone who can take you out to a pond and then to a stream. if you've been fishing for a while, you already know where fish are, but now you need to know how to present a fly to them. In addition, while poppers are basically the same whether spin or fly, the power of fly angling is to be able to present something in a way that can't be done with other gear.

when those stocked trout have switched over to feeding on bugs and your rapala or mepps gets ignored, you know its time to break out a drifted woolly bugger or nymph. when you see those subtle rises underneath an overhanging bush, you will learn how to present a dry fly, perhaps with a trailing emerger.

have fun with it! while you can eventually learn all this on your own and via youtube or other online materials, talking with someone or, better yet, getting out with someone will really help speed up the process!