• Check the fragmentation of all indexes by using sys.dm_index_usage_physical_stats.

    If the fragmentation is more than 35% --Rebuild all the indices.

    Ask the users about any change of code..? If so, Check for missing indices by using sys.dm_missing_index_details.

    or else, save the SP to .sql file and open DTA(Database Tuning Advisor) and load this .sql file under workload option select your database from the list which shows below and click on Start Analysis, If you got the recommendations more than 65% apply all the recommendations provided SQL Server.

    Thanks,