Lay the piece of iron-on interfacing on the work surface, treated side (the side which is SUPPOSED to stick when you iron it) facing up.
Begin on the front sections first, and work from the top down.
Start at the top area of one of the fronts – the part that looks like a shoulder or folded wing. Take one of the graduated strips of fabric and fit it to the ‘shoulder’ on about a 45 degree angle, with the narrower end towards the inner edge, and the wider end towards the outside edge.
Do the same on the other side.
Do the same with the next fabric strip. Work your way down the front sections, using your graduated fabric strips up first. You began at the top by placing the first strip on an angle; the strips should gradually become horizontal by the time you reach the upper middle section. Keep adding strips all the way to the bottom of the flaps, trying to keep both sides even.
Make sure that the last fabric strip is placed slightly lower than the bottom of the interfacing flaps – it looks better this way, when it’s turned. Pin the fabric strips to the interfacing base.