My article related to Getting started with SQL Server database diagrams is published on following address. Due to copy right restrictions i will not publish it here. You may visit it at Getting started with SQL Server database diagrams. It would be very helpful to start effectively working with Database Diagrams in SSMS.
Data Modeling and Database Design, Database Diagrams, dbDigger, Publications of Atif Shehzad on MSSQLTips.com, SSMS tips and tricks