Apple has published official Ping usage guidelines for artists which describe exactly how to create an artist profile and begin posting content.
According to the guidelines [PDF], artists are encouraged to hold off on creating a profile until they have several posts ready to go, because "Fans will be far more likely to follow you if they can tell that your profile is active." I agree with Apple there. Additionally, artists are encouraged to submit videos (2GB max), as long as they're in .mov, .m4v or .mp4 formats. Apple also suggests that artists create videos with iPhones whenever possible.
Apple also lists what's not allowed on an artist profile, including "...pornography, hate speech, racism, nudity or drug use."
Most of the artists I follow are relatively quiet, with notable exceptions like Jack Johnson. Some users have panned Ping, but I've found the 10.0.1 iTunes update to make it much more enjoyable.