What to adjust here to tune parallelism

 Hi Experts,
We are seeing lots of parallel related wait events in our data warehouse database. I queried the database but don't know what to adjust with the following selected output info. Could you help?

Thanks.
Yinhai
SQL> show parameter parallel

NAME                                 TYPE        VALUE
------------------------------------ ----------- ------------------------------
fast_start_parallel_rollback         string      LOW
parallel_adaptive_multi_user         boolean     TRUE
parallel_automatic_tuning            boolean     FALSE
parallel_execution_message_size      integer     2152
parallel_instance_group              string
parallel_max_servers                 integer     160
parallel_min_percent                 integer     0
parallel_min_servers                 integer     0
parallel_server                      boolean     FALSE
parallel_server_instances            integer     1
parallel_threads_per_cpu             integer     2

NAME                                 TYPE        VALUE