No can complain that we're not being constructive now, because we're providing links to writing resources!
For information on how to create interesting original characters for roleplay or fanfiction, you can try Elena779_2000's Character Style Sheet. It's not guaranteed to be 100% effective, but it may help a bit. Also, it's written by Alina, so you'll still have to put up with her sarcasm. Ha ha.
There are tons of websites out there that deal with RPG etiquette and bad roleplaying characters, but here are a few:
As for Fanfiction, Writers University is a very comprehensive look at all facets of Fanfiction and how to write it. There's even a section on how to deal with flames that some of you may be interested in looking at ;). The site is currently being moved to here, but that site is mostly a jumble. Use the old link for now.
Good Matrix fanfiction can be found at The Construct. End of story.
Alina also highly recommends the Protectors of the Plot Continuum - a site devoted mostly to dealing with Lord of the Rings Mary-Sue fanfiction woes, but is definitely the most hilarious and canonical take on dealing with the troublesome little buggers. Fight bad fanfiction with good fanfiction!