The first thing to do when tying GT knots is to have a rock solid fixed point so swivels and loops can be fitted over and pulled on HARD, try a cup hook screwed into somthing solid.
Ok here goes, after twisting back the twisty onto itself you should have a magically neat and cool looking 4 strand leader, might as well put a swivel into this section before starting the back twist. On finishing the doubled section, hook the swivel onto your fixed point, then loop the tag end back and around 4 strand line as you would if you were tying a uni knot, take tag through loop 3 times(tag is being taken through loop back toward the rod end of leader-just imagine a uni) then gently close the knot teasing the knot back up toward the swivel to ensure that the formed knot remains on the 4 strand section. Once the knot is mostly closed, take a couple of wraps of standing line in one hand and the tag in pliers and pull knot closed (lube of course) using equal pressure in both hands, this is pretty important as sustantially uneven forces in either hand can ruin the knot.
Long winded to explain but quick and easy to tie.
Neil