Clearing Cache for SQL Server Performance Testing

USE <YOURDATABASENAME>;
GO
CHECKPOINT;
GO
DBCC DROPCLEANBUFFERS;
GO

this tip is copied from 
http://www.mssqltips.com/sqlservertip/1360/clearing-cache-for-sql-server-performance-testing/ 

use

DBCC FREEPROCCACHE 

[ ( { plan_handle | sql_handle | pool_name } ) ] [ WITH NO_INFOMSGS ]

to cleanup plan cache