Lay your serviette out flat and square before you. Take the top left and right corners and bring them down to the bottom left and right corners so that it is folded in half horizontally with the crease at the top.
Take the top right hand corner (where the crease is) and bring it to the center bottom point if the rectangle shape. Repeat with the top left hand corner. You should now have a triangle shape with a vertical gap running down the middle.
Take the corner of the right loose flap that just folded down (it's in the bottom centre of the triangle) and fold it back on itself so that what *was* the middle line is now matching the outside edge of the triangle. Repeat with the left side loose flap. You should still have a triangle shape but it now looks like a triangle with a shirt collar LOL.
Take hold of the serviette at the top point of the triangle and at the bottom centre of the triangle and and raise it so that it stands proud of the two collar pieces on each side.
IF you have paper serviettes, there will be a pre-formed factory made crease along this centre line (of the last step) and because of it the serviette probably won't want to stay raised in the middle, so bring the centre in towards itself until the bottom parts of the collar meet and then gently press the top bit down so that you have a top triangle with the crease in the centre. I found that by creasing the outer pleats of this top triangle, it did stay raised up.