Tuning Stored Procedure

Most of the time I come accross the thread wherein user has requested to get started with stored procedure performance tuning , so here are some good reference material for tuning stored procedure and optimize stored procedure for performance
http://www.sql-server-performance.com/tips/stored_procedures_p1.aspx, http://www.sqlservercentral.com/articles/Performance+Tuning+and+Scaling/performancetuningstoredprocedures/2505/ and http://searchsqlserver.techtarget.com/generic/0,295582,sid87_gci1247499,00.html