How to get list of the most expensive queries in SQL Server

SELECT TOP 20
    (total_logical_reads + total_logical_writes) / execution_count AS AverageIO
    ,(total_logical_reads + total_logical_writes) AS TotalIO
    ,qt.text Query
    ,o.name ObjectName
    ,DB_NAME(qt.dbid) AS DATABASEName
FROM 
    sys.dm_exec_query_stats qs
        CROSS APPLY
    sys.dm_exec_sql_text(qs.sql_handle) AS qt
        LEFT OUTER JOIN
    sys.objects o ON o.object_id = qt.objectid          
ORDER BY AverageIO DESC