First, as Thales has said, "Know thyself". Before you start on your journey of self branding, it very important for you to know how people perceive you and how you perceive yourself. Start with self-discovery.
1. Know what you want online: what you want to achieve and how you want to be know for
2. 15 Second Elevator pitch: "Who are you? What you do?"
3. Have a blog / website in your name: Cover your industry like no one else
4. Profiles on Top 4 Social Networking sites: Facebook, MySpace, Orkut, Twitter - In your name preferably
5. Profiles on Career Networking SItes and wherever your peers are: e.g. LinkedIn
6. Multiple e-mail addresses: One for work: One for Personal; One for Spam
7. Multiple IM accounts: + Meebo account
8. Public resume: as a blog post
9. Video resume: 3 minutes length on Youtube
10. Presentations on your field on Slideshare.net
11. Create Your Own Social Network: Use Ning
12. SEO: Promote your content - great headlines, lists, submit your links to all social news sites
13. SMM: Creating content that users of social media sites such as Digg or Facebook like. Things that do well are: top 10 lists, funny, sexy, parody, celebrity...
14. Create your own event: Online example - Blog Carnival - getting people to contribute posts on a topic; Offline: organize an event; promote it online through blogs, social networking sites
15. Create an eBook: 50 pages maximum on your industry. Give it away for free. Mention the link in your resume, blog, profiles...basically, as Seth Godin has said, be everywhere.
16. Participate on all sites where you are a member: e.g. Submitting and rating stories on Digg, Reddit; bookmarking favorite links on del.icio.us; friending people on Facebook, Following people on Twitter; posting often; comment on blogs. Of course, all this is only possible when you listen to what people are talking about currently and reading other people's stuff.
17. Make yourself useful: e.g. answer questions on Yahoo Answers, LinkedIn
18. Accounts on Forums for your industry, if any: Search Bigboards.com for forums in your area. Participate at least once a week. Answer other people's queries for advice.
19. Crosspost: Promote your articles or any updates across all other sites where you are a member but do not spam. Once in a while is okay.
20. Update your data across all the above sites periodically.
Other personal branding ideas: great looking wardrobe, business card, testimoniais and references...whatever builds your story, use it.