The costume consists of a (preferably dirty) old-fashioned pantaloon with frills at the wrists, shins, and around the neck. Three red pom-poms adorn the front of the suit, as well as the tips of the toes on the tall shoes. Masks of Pennywise can be found for purchase, or you can instead simply paint your face in the same designs and buy a wig or temporarily dye and style your hair. A red balloon or an origami paper boat can make for great accessories to the costume and may give you the touch you need.
A couple or pair of friends can even mix it up by going as both this and the Tim Curry version side-by-side.
As a word of caution, due to a few years worth of "scary clowns" in the media, you may want to wear this costume with an air of caution, as some people may not recognize it as a character and consider you one of the harassment clowns that are occasionally seen throughout the rest of the year.