ok first the disclaimer stuff its difficult to teach
you a technique via the net if you do not get it right you
can fall out and die if the harness is not done correctly
or if it is not tight enough it is dangerous.you need
professional and personal instruction on how to do this properly
and you need to practise it try hanging in it for a period
of time to realy get the feel(pain)also try inverting.

ok first you will need 5 meters of rope grab
aproximately the middle of the rope as shown in the photo below

reach behind your right leg and grab the right side rope
bring it around your leg under and through the crotch loop
i normally then throw it over my right shoulder you
need to do the same with the left side and when you are finished
it should look like the photo below

next on the end of your right hand side you need to put a
figure 8 on the bight.sorry this is a bad illustration
because i did not leave enough tail on the knot to do
a stopper knot.make sure you do

next pass this knot and the right side rope around your waist
to the right first keep the rope above your hips.adjust your
harness so that the knot ends up on your left hip.

next run the left side rope around your waist keeping above
your hips to the left first untill you get back
to the figure 8 knot.clove hitch on to the figure 8 knot
adjust for tightness make sure to put stopper knots
for the clove hitch because it is designed to slip
it is very important that you clip to both the crotch loop
and both waist loops as shown in the photo below