Use DMVs to determine based on past executions which indexes would be beneficial in that database.

The following SQL should be run in Production SQL server (off hours). It basically uses DMVs to determine based on past executions which indexes would be beneficial in that database. It recommends what indexes could be created on the specified tables.

SELECT
 migs.avg_total_user_cost * (migs.avg_user_impact / 100.0) * (migs.user_seeks + migs.user_scans) AS improvement_measure
 ,
 'CREATE INDEX [missing_index_' + CONVERT (varchar, mig.index_group_handle) + '_' + CONVERT (varchar, mid.index_handle)
 + '_' + LEFT (PARSENAME(mid.statement, 1), 32) + ']'
 + ' ON ' + mid.statement
 + ' (' + ISNULL (mid.equality_columns,'')
 + CASE WHEN mid.equality_columns IS NOT NULL AND mid.inequality_columns IS NOT NULL THEN ',' ELSE '' END
 + ISNULL (mid.inequality_columns, '')
 + ')'
 + ISNULL (' INCLUDE (' + mid.included_columns + ')', '') AS create_index_statement
--, migs.*, mid.database_id, mid.[object_id]
FROM sys.dm_db_missing_index_groups mig
INNER JOIN sys.dm_db_missing_index_group_stats migs ON migs.group_handle = mig.index_group_handle
INNER JOIN sys.dm_db_missing_index_details mid ON mig.index_handle = mid.index_handle
WHERE migs.avg_total_user_cost * (migs.avg_user_impact / 100.0) * (migs.user_seeks + migs.user_scans) > 10
ORDER BY migs.avg_total_user_cost * migs.avg_user_impact * (migs.user_seeks + migs.user_scans) DESC