The blood knot is one of the best for joining monofilament of similar diameters. With light lines differences in diameter are less critical and the blood knot is commonly used for making tapered fly leaders. When you first tie this one you may feel like you need twenty fingers, but you’ll quickly get the hang of it.
1) Lay the lines parallel and facing in opposite directions and cross the end of one over the other. Wrap this line three or four times around the other and place the end of this line in the crotch or the V formed by the two lines.
2) Do the same with the other line, being sure to pass the end through the loop in the opposite direction to the first line.
3) Slowly pull on the standing ends of the lines to draw the knot together. When the knot is formed, lubricate with saliva and pull the knot up tight.
4) Trim the tag ends off so that they don’t catch in the rod guides.