While some people I know are afraid of clowns, others (children, mostly) are delighted by them.
Clowns are people that traditionally dress up in baggy clothes with mismatched colors. They paint their faces and entertain children. As with most Jobs, there are certain skills that a clown must perfect in order to be among the best in his field.
Perhaps the most memorable thing about clowns is the look. A successful clown has to be dressed (im)properly for the occassion. Traditional harlequin dress includes big, red shoes, a plastic red nose, a party hat, baggy clothing (polka dots aren't required, but they're better than say, stripes), and face paint. Different clowns paint their faces in different ways, but when we think of clowns, we think of a white-faced man with a big, red smile.
It's not just about the clothing, though. A proper clown must also be able to clown around. Typically, clowns make balloon animals, do slapstick comedy, make funny noises, ride small bicycles, and do magic tricks. The classic balloon animal is a giraffe, but expert clowns can model things like redwood trees and a 1:1 scale of a water molecule.
Clowns have to like people. A clown with a short temper might ruin someone's birthday party.
If you're looking to stray away from being a conventional clown, you could be a mime or have your own shtick. Buffo, the world's strongest clown, is a good example of this. Or you could specialize in mentally-handicapped rap music clowning. According to an AOL Instant Messenger profile I saw once, there are also clowns that eat people while they sleep. Some people...