Performance is very Slow in query

[papa]

Hi experts!

How to increase performance for the following query BSIS?

select    a~saknr b~txt50 
            into corresponding fields of table it_table
            from skb1 as a
            inner join skat as b
            on a~saknr = b~saknr
            where a~saknr in v_variable
            and   a~bukrs eq company.

  
if sy-subrc eq 0.select bukrs hkont augdt
                  augbl zuonr gjahr 

         belnr buzei
         
         budat
         werks
         kostl
         aufnr
         shkzg
         dmbtr
         prctr
         into corresponding fields of table it_bseg
         from bsis
         for all entries in it_final
         where bukrs eq company
         and   prctr eq s_center
         and   gjahr eq s_gjahr			   							
         and   hkont eq it_table-glcode
         and   budat in s_budat                    "BETWEEN fromdt AND todt.

Any idea to better this query?