Improving SP performance using Non Clustered Index.

Question

Hi Team,

I need to improve performance of a SP which is in a Database in SQL Server.

1.One of the Select query uses a Table, which is having clustered index on Column A. This table is joined with other tables on columns A,B and C(all are columns of same table). I am planning to create a Non Clustered index using columns A,B and C. Please confirm if this will improve my SP performance, I want to be sure on this as one of the column that is to be used in non clustered index is A on which a clustered index is already used.

2. I have to use a filter LIKE '%ABC%' which is slowing the query, could you please let me know how could I improve the query performance here. I surely need to use %ABC%.

Please let me know if more details are needed.

Thanks,

Salil