Generally it is because of Blocking, space issues, IO issues, Index maintenance (Fragmentation), Update stats,High CPU Usage, High Memory Usage.
Check the execution plan of the query and confirm whether it is using table scan or index scan
Check the missing indexes
If table scan is followed suggest them to create necessary indexes.
Check for number of joins used in query and eliminate un necessary joins
Check for fragmentation and fix it if exists
Thanks,
I’m nobody but still I’m somebody to someone………….