Tools
Dribble: Twitter for DesignersYou can't actually sign up yet. The web site just came out of private beta over the weekend and is still limited to invite only. However the concept seems really sound and its something to keep an eye on.
If you would like to try for an invite you can post your portfolio to featural.com.
Facebook - Yeah. Most everyone has one but more and more often Facebook is being used by clients and employers to find out more about the people they are hiring.
Linked In - If you don't have a LinkedIn account you should get one. Keep an up to date list of your work. Recruiters often use LinkedIn to find people with the exact skill set they are looking for to fill a new position.
Twitter - I have mixed feeling on twitter. It can be used as an amazing networking tool but it can also be very very annoying. Some of the following articles discussing social media networking using twitter.
Articles
Clients
Identifying and Dealing With Different Types of ClientsSecret to Landing Clients nearly 100% of the time
3 Simple Ways to Create Client Loyalty
Resumes
7 Ways to Spice Up Your ResumeFunniest Resume Mistakes
Professionalism
Common Questions about design professionalism7 Ways to Build Trust on a Portfolio Site
Social Media
25 Ways to Engage Contacts in Social MediaUsing Twitter for Business
General Networking Tips
10 Game-changing Tips from the World’s Top Freelancers5 Things I'd Tell my 21 Year Old Entrepreneurial Self
5 Reasons to Network in a Touch Economy
Avoid These 10 Networking Blunders
and finally 10 Ways to get myself into the studio and working. My favorite, #10 - Have a chocolate chip cookie waiting on my work desk