Use the Correct Leader and Tippet for the Job
Modern tippet and leader material is amazing stuff when you think about it - a virtually invisible link between angler, line and fly - how cool. It's much better than braided horse hair or silk, the standard fly line and leader materials available until less than 100 years ago, and much easier to acquire I must say.
With all of the advanced leaders and tippets out there today it amazes me how many anglers limit their fishing by only using one type, size, and material type all the time. I realize it's easier to find your favorite set up and stick with it, and being comfortable casting and fishing a certain leader is important to a point, but not if it limits your fish catching ability.
Here are some suggestions for specific leaders and tippets for specific situations:
1. Nymph fishing - I nearly always use flourocarbon leaders and tippets for fishing nymphs. They sink faster and have much less visibility under water than standard nylon monofilament. In addition, using a mostly flat leader (not tapered) will also help your flies to sink faster and get into the fish catching zone earlier in the drift. Since the perfect nymphing leader isn't currently being manufactured, you will have to build your own mostly flat nymphing leaders from flourocarbon tippet material. I use slightly different tapers but usually start with about 12-18 inches of 0X for the butt section, go down to 12 inches or so of 2X, then use about 7 to 10 feet (depending on depth) of 3X or 4X for the main body of the leader.
Sidenote: Rio does make a sinking mono leader, the VersiLeader, that I have not yet tried. This may address the buoyancy issues with nymphing standard monofiliament, but I'm hesitant to recommend it until I fish it. Maybe someone could reply with their experience with these leaders.
2. Dry fly fishing - I generally use a factory tapered monofilament leader for dry fly fishing. In my mind the absence of knots on these factory tapered leaders overcomes whatever strength inconsistencies may occur in the extrusion process. No knots generally means less likelihood of tangles or picking up algae.
I like 9, 10 and 12 foot leaders depending on the situation. I generally fish 4X or 5X leaders with an 18-24 inch tippet on the end of that. If you use the 12 foot leader with 18-24 inches of tippet you'll have to practice casting it. A smooth yet powerful cast will get the job done.
3. Dry dropper rigs - I use the dry fly leaders mentioned above, usually with a flourocarbon dropper of 12 to 48 inches, depending on depth and the situation.
4. Flats Fishing - I recommend a good saltwater flourocarbon leader for flats fishing for many of the same reasons I use flouro in nymph fishing - less visible and sinks faster. In addition, flourocarbon leaders are much more abrasion resistant than nylon mono. All of the shells, coral, and little rocks you encounter in saltwater fishing can be hard on a leader and flouro stands up better.
5. Toothy fish - Be absolutely sure to use either a wire bite guard at the end of your leader or use TyGer wire leader material, which is nice because it can be knotted.
6. Sinking lines and sink tips - When fishing a sinking line or sink tip line it is not necessary to use a long leader. I like to use about 4 to 6 feet of flat 2X or 3X flourocarbon. Some manufacturers also produce a short sinking line leader. If you determine that you like or need a bit of a taper for easier casting you may go with one of these options as well.
Leaders and tippets are one of the most overlooked aspects of fly fishing. Using the right leader for the job should help you catch more fish. Hope to see you out on the water fishing the right leader.