Here's the low down on leaders:
1. If you want a long leader whatever you do don't just get a tapered leader and add lots of tippet. The final tippet section of your leader shouldn't be any longer than 2 feet. Long tippet section area really difficult to turn over especially with bushy dries and when on the water can end up causing more drag as the wayward loops get caught in currents. Better still take a tapered leader with a long butt section (like the trout hunter leaders which are around 70% butt section to tippet) then add a heavy section of leader material ie if you are wanting to end at 6lb then extend out a section of 10lb and lastly tie on your short section of 6lb on the end.
2. Setting your knots properly is important, you would have been told to wet the knot first which is important, the other thing to do is to make sure you pull it tight slowly. By quickly tightening the tippet you'll create friction and heat which will weaken the tippet.
3. The biggest breakthrough in recent years has been the creating of ultra low diameter fluorocarbons like the trout hunter fluorocarbon. Basically these lines are such a breakthrough because they allow nymph fishers to get flies deeper with less weight due to the reduced resistance from the low diameter tippets. For the dry fly fishermen the Trout Hunter tippet is as supple as a copolymer whilst being lower in diameter and less visible to the fish.
Note: Rene's pet hate in terminology. Both fluorocarbon and nylons are called monofilaments (ie they have one filament) alternatively you can get multi filament lines like braids or fused superlines.