Because Jane at DearAuthor knows her stuff, and is far more articulate than me in the morning, I direct you to her awesome list of things you should not do while promoting yourself on the internet:
10 Author Online Promotional Don'ts
Agent Janet Reid also has some excellent advice on how not to conduct yourself at conventions and writing conferences:
Finally, this video has nothing to do with promoting yourself, online or otherwise - unless you're wondering what an effective viral video looks like (and you need a good laugh). If you're even passingly familiar with the X-Men, you'll get it:
Wolverine in 30 Seconds
Have a nice day!