To improve a insert SQL

We have a insert SQL that we want to know if there is a way to improve the query.  The SQL has a unique index constraint on the insert.  Here is the the SQL:

         insert

            /*+ append */

         into cust_ship_to_loc

            (

               cust_ship_to_loc_sqn,

               sys_cde,

               eff_start_date,

               rec_srce,

               cust_ship_to_sqn,

               loc_sqn,

               proc_isrt_date

            )

         select intgn_sqn.nextval,

            s.sys_cde,

            i_eff_start_date,

            k_vu_cust_ship_to_source,

            s.cust_ship_to_sqn,

            --nvl(l.loc_sqn, -1),

            nvl(l.loc_sqn, get_missing_loc(i_systems(i) .sys_cde)),