Folding and Curling
From DT Online
To fold a stiff piece of paper or thin card, lay a ruler along the edge to be folded up. For heavier, stiffer papers that may not have been pre-creased, try using two rulers. This technique is very useful where two parallel creases have to be made close to each other.
To form crisp, firm creases cover the folded card with a clean piece of scrap paper and burnish with a smooth surfaced ruler.
Roll or pull paper or thin card gently under a ruler to give it a natural curve. Paper pulled through firmly against a ruler will give very curly streamers.