How can you increase SQL performance?
1)Keep your indexes as narrow as possible. This reduces the size of the index and decrease the number of reads needed to read the index.
2)Try to create indexes on the columns that have integer values rather than the character values.
3)If you create a composite (multi-column) index, then the order of the columns in the key are much important. Try to order the columns in the key as to enhance the selectivity, with the most selective columns to the leftmost of the key.
4)If you want to join several tables, try to generate surrogate integer keys for this purpose and create indexes on their columns.
5)Create the surrogate integer primary key (identity for example) if your table will not have many insert operations.
6)The Clustered indexes are more preferable than nonclustered, if you require to select by a wide range of values or you need to sort results set with GROUP BY or ORDER BY.
7)If your application will be performing the same query over and over again on the similar table, consider creating a covering index on the table.
8)You can use the SQL Server Profiler Create Trace Wizard with "Identify the Scans of the Large Tables" trace to determine which tables in your database may need indexes. This trace will show which tables are being scanned by queries in spite of using an index.