One of the best-known books on ADR in Washington is Alternate dispute resolution deskbook : arbitration and mediation in Washington published by the WSBA.  However, this resource has not been updated since 1998.  What’s a lawyer to do?  Come down to the library and check out these recent CLEs:

Finding success at mediation : skills that make a difference / WSBA.
KF 9084 .A75 F56 2008

Alternative dispute resolution for family law cases : staying out of court / WSBA.
KF 9084 .A75 A47 2007

Emerging trends in dispute resolution / WSBA.
KF 9084 .A75 E44 2007
 
The essentials of civil settlement strategies / WSBA.
KF 9084 .A75 E87 2006

Winning without trial : effective strategies for success before trial / WSBA.
KF 8900 .W56 2005