Library Cache Get Hit Ratio Is Always Low

Hello,

1 Buffer Cache Hit Ratio         99.92
         1 Chained Row Ratio              .01
         1 Database CPU Time Ratio        98.932
                                          123135
                                          3539

         1 Database Wait Time Ratio       1.0678
                                          768646
                                          4606

         1 Dictionary Cache Hit Ratio     99.54
         1 Execute Parse Ratio            85.35
         1 Get Hit Ratio                  6.09
         1 Latch Hit Ratio                100
         1 Library Cache Hit Ratio        99.97
         1 Parse CPU to Elapsed Ratio     99.33
         1 Pin Hit Ratio                  97.49
         1 Soft-Parse Ratio               94.14

Above is from my DB instance(Oracle 10.2.0.4 EE) on Windows Server 2008. I run a sql script to get this.  Get hit ratio is always below 10% no matter when I test it. What part should I tune? Recently I have done Keep Pool sizing,and monitoring,database buffer sizing and monitoring, set session_chached_cursor=100,rowed chained removed,defragmented indexes rebuild , shared pool sizing and monitoring etc.  I don't use AMM(automatica SGA Memeory Management).