Well, you can buy the fancy knotless tapered leaders or just buy spools of 15lb, 8lb, and 6lb. Use bloodknots and attach the 15lb to your fly line, then go 8, then depending on the fish you can go down to 6. The main reason for using fluorocarbon is for its' lack of memory and it's super clear in the water. You can then get away with non fluoro for the 15lb. Other than that it really depends on the fish, ive listed below what i usually use.
Salmon - 15lb about 3ft, 10lb about 3ft - 8 lb fluoro 3 feet
Steelies - 15lb " " , 8lb about 3 ft if im in a river or 6ft if im in a creek, 6lb fluoro if really clear river
Trout dry fly fishing - 15lb - 8lb - 6lb - 4lb, the 4lb you can use fluoro for nymphing or non fluoro for dries
Bass - usually just go stright 8lb fluoro, usually the dry flies are pretty big for bass so they wont sink anyways
Also, when you fish dry flies a really deadly technique is to 'skirt' them across riffles. So just kind of hold all the line off the water so the only thing touching is the fly, then drag it across wherever you think fish are. I usually change my leader a lot. Sometimes even between holes. I might be nymphing a faster run with a shorter heavier leader then when i get to a deep slow pool ill throw on a few extra feet of 6lb test.
