Before specifying an index in queries:
Check showplan output for the “Keys are” message to be sure that the index keys are being used as expected.
Use dbcc traceon(302) to look for other optimization problems.
Run update statistics on the index.
If the index is a composite index, run update statistics on the minor keys in the index, if they are used as search arguments. This can greatly improve optimizer cost estimates. Creating statistics for other columns frequently used for search clauses can also improve estimates.