Glue a red felt hat cap on his head. Then at the middle of the bigger ornament, glue a strip of black paper to serve as his belt. You can glue a patch of black felt at the bottom to serve as the base, and Santa's boots. Make all of the body parts look like Santa Claus with bits of felt or coloured paper.
However it is important to know the different types of clip art that are available, with most clipart sites being filled with old scanned artwork that isn't very attractive. In fact a Google search for free clipart is likely to find dozens of sites filled with black and white drawings from the 1970s that was scanned and uploaded. Unfortunately this type of image isn't easy to adjust the size or manipulate.
Do make sure your cartoon advertising character is executed in a variety of poses so you can use him in a wide array of applications.