Taking the 20cm tag of the lighter line, wrap it like a bed spring around the doubled leader, starting close to your pinching fingers and wrapping towards the folded end of the leader/heavier line.

It really makes your life easier if you keep the loops tidy and close to one another, taking care not to cross over any previous loops. You will need between 10-20 wraps depending on the weight of your main line, with finer line requiring more wraps, heavier less.

To complete your knot, feed the tying line through the folded heavy-line loop, making certain that it exits the loop on the same side it came in, ie. if you fed the main line in from below the loop at Step One, it must follow back out the same way. IF you have the line come in from one side of the heavy loop and exit across the other direction, YOUR KNOT WILL FAIL. 

Move your hands so that one is holding both leader strands and the other is holding both main line strands. Pull gently away from one another until the knot starts to tighten. Wet the knot with saliva to lubricate before releasing the tags and gently but firmly pulling the leader and main line against one another until the knot is “locked”.

Trim mono or flourocarbon lines as close to the knot as possible, without nicking the knot. Any excess line here has an annoying habit of catching on runners and hampering your cast. With braid, you can leave a few millimetres of tag, as it is soft and will not catch. This allows for a little bit of “slip”.