Here is a short comment on Legal Ethics Forum on lawyers and social media. It discusses five basic rules to keep in mind:
(1) make sure you don't disclose confidential information
(2) be careful when interacting with third parties
(3) don't lie
(4) don't try your case on the 'net/press
(5) don't criticize the court.
For previous posts on issues related to social media, go here, here and here.