This is undoubtedly the best way to practice fly casting while actually fishing. I assure you it's one hell of a lot of fun. Try everything: anti-drags, anti-obstacles, curves, hooks... In certain stretches, fish with only roll casts. You'll realize the versatility and practicality of this superb cast. Practice accuracy. Get your fly right up against the bank under those branches and in front of that promising rock. Experiment in currents with a variety of slack line casts and find out how far you can get your fly to drift with each kind of cast without dragging.
The reach cast
This type of cast isn't included in any specific category since it's a cast that solves a variety of situations. Acknowledged by the North American master, Doug Swisher, as the most powerful tool in his technical arsenal, the reach cast is in itself an anti-drag, anti-lining and anti-obstacles cast. That's all.
You'll discover that no matter how many different presentation casts exist, the number and variety of different current configurations is always infinitely greater. The other discovery you'll quickly make is the enormous and still under-valued importance of drag (and that will motivate and stimulate you to grow as a fly caster, ...or the opposite). Every now and then, make a long cast. With the fly fifteen yards away (in a stream, that's very far), achieve the drift of your life (if you had an audience, you'd get applause). Expect to hang up more than ever. On overhanging branches, stones and especially on all sorts of things in back of you. Since you're constantly changing position and angle, your backcast becomes a magnet for all kinds of vegetation and obstacles. Get used to looking back regularly.
In this fishing mode, there's no place for lazy hands or minds. Either you're on the ball with your line hand or you won't hook a fish. The long retrieve (arm fully extended behind your back) and the roll-cast pickup allow quick, accurate line manipulation. Leaving your retrieved line at the mercy of the current is slow and gets tangled on stones, twigs and waders as you advance. Hold it in loops in your free hand as you retrieve it.
In this respect, I can only mention something interesting about the leader. The rest is absolutely irrelevant. You want your leader to be as short as possible (nine feet?), as thick as possible (5X?) and with the least possible number of knots (none?). Remember you're going to be making an awful lot of casts to very complicated lies. A leader like this will save you many a tangle. It'll give you more accuracy and, if you've got a headwind, you'll remember me and this advice. Knots on leaders have the habit of catching a lot of green stuff, which makes them heavier. Then, if you try to make a puddle cast with the slack at the end of the line and at the leader (ideal for eddies at the bottom of boulders), you'll end up with a rat's nest. One more thing about the gear. I learned this from Lefty Kreh (one of his books). Caps with very wide visors give good shade but hinder your view of the path of the line in the air at a certain height. When fishing the water, this can be a little drawback for tracking where your fly lands. Ah! I almost forgot, it's so self-evident: waders with felt and spikes on the soles. Like I said, you'll be moving pretty quickly.