I have a range partitioned table that contains close to 100 million rows.

This table has a primary key and 12 non unique global indexes. I did not
design the table, I inherited it.

Is there a rule of thumb to follow as to whether the indexes on this table
should be changed to local instead of global indexes? In addition, would
I be better off converting the indexes to parititions.

This table used for ADHOC queries so examing every explain plan would be
an arduous task therefore I am looking for general rules to follow.

Are global indexes better than local indexes or vice versa in this situation.
Or is there some queries I can use to determine the best method to
organize my indexes.

Thanks to all who answer.