I tie my own tapered leaders using Stren High Impact leader material, but many other brands do the job well too. Take a 5-foot length of 30-pound-mono line and attach it to the end of the fly line. This represents the butt section. To the other end tie a 2-foot piece of 20-pound line, using either a blood knot or a double surgeon's knot. Tie that to a 2-foot length of 15-pound line. You can stop there or add another section of 12-pound line, as you prefer.