Useful queries for optimizing Sql Server 2005

Question:

How can I figure out the queries that take most resources on a server.

Answer:

We use this query.
It lists the worst queries (I/Os) on your database since the last restart.

select top 5 (total_logical_reads/execution_count) as avg_logical_reads,
(total_logical_writes/execution_count) as avg_logical_writes,
(total_physical_reads/execution_count) as avg_physical_reads,
Execution_count, statement_start_offset, p.query_plan, q.text
from sys.dm_exec_query_stats
cross apply sys.dm_exec_query_plan(plan_handle) p
cross apply sys.dm_exec_sql_text(plan_handle) as q
order by (total_logical_reads + total_logical_writes)/execution_count Desc

I grabbed it somewhere form TechNet: Monitoring SQL Server health