I recently came across very nice article about optimization tips for SQL Server 2005. Here is the list of those 12 tips.
Twelve Tips For Optimizing Sql Server 2005 Query Performance
1. Turn on the execution plan, and statistics
2. Use Clustered Indexes
3. Use Indexed Views
4. Use Covering Indexes
5. Keep your clustered index small.
6. Avoid cursors
7. Archive old data
8. Partition your data correctly
9. Remove user-defined inline scalar functions
10. Use APPLY
11. Use computed columns
12. Use the correct transaction isolation level
Reference : Pinal Dave (https://blog.sqlauthority.com) , Original Article