Facebook:First things first, make your profile private, logout, and view it. Go over it with a fine tooth comb. What do you "like"? Any embarrassing likes left over from Highschool/college years? Make sure you change the settings on embarrassing/incriminating photos. I know the memories may be precious to you, but a future employer doesn't want to see photos of you doing keg stands at the frat party senior year. I personally don't really use Facebook to network professionally beyond making friends with my colleagues.
LinkedIn:If you don't have LinkedIn yet there's a problem. It doesn't matter what kind of professional you are, this one is a must.
About.me:Your address on the web where you can direct people to what matters most to you. About.me is one of the top results on google when someone searches your name so it's worth filling out a profile.
Branded.me:This website also allows you to publish content and connect with other users, like a more long winded twitter.
A personal website:
Having a personal website for yourself is one of the best ways to rank for your name on the search engines. It doesn’t need to be robust. It can be a simple two to three page site with your resume, link to your social platforms, and a brief bio. You can always expand on the website with time. GoDaddy and other hosting sites frequently offer deals on domain names. These guys are currently offering 50 cent domains.
Twitter:There are a lot of plug-ins that allow you to auto-generate statuses and link content thru Twitter. The more you post the more people pay attention.
Google:Google yourself and setup alerts for your name on a regular basis. Have a fairly common name? Consider using your middle initial or middle name to differentiate. Cultivating a strong personal brand is just as much about being responsive to what is being said as it is about creating intellectual property.
An additional note here is to join Google+ groups.
1. Stay active
2. Create a consistent look and feel.
3. Reserve your name everywhere (even if the site isn't of use to you right now)
4. Develop a strong positioning statement.
5. Store links of all your social media profiles in a spreadsheet.
6. Limit your areas of "expertise" to around 3 key items.
7. Define and pursue an objective.