There are no rules. However, some are better received than others. Here are some tips from what I have observed:

• Portability affects how well the code is received.
• use strict- and use warnings-friendly for bonus points.
• But most important by far: It must have artistic element to be interesting, and I don't mean simply formatting the code to look like something. Just look at Obfuscated Code and figure out what you like about your favorites.