My cousin Cathy with the giant pompoms we made as decorations for her wedding this Saturday.
To make them you just need to layer around 10 sheets of tissue paper (we used A3 sheets and alternated colours but you can make them any size or colour you like) and then make 1 1/2 inch accordian folds, creasing with each fold.
Then you snip off the ends in a round or pointed shape and twist some wire around the centre to keep the folds in place. It should look like the picture below. It's easiest to attach a length of monofilament (otherwise known as fishing line) to the centre now as well.
Then you fan out the folds (see below) and separate each layer, pulling each one away from the centre. And that's pretty much it. Just hang from the ceiling at any wedding or party and wait for the ooohs and aahs from your guests.
And here's how the pompoms should look once they're hung in the marquee - image courtesy of the amazing Martha Stewart.