For Datafile I/O Statistics, you can refer V$FILESTAT joined with V$DATAFILE. Columns from v$filestat useful are phyrds (No of physical reads done), phywrts (No of physical writes done) After startup of database.
This is vast topic to discuss, you can mainly concentrate on full table scans. You can create index after checking full table scans, and reduce # of full table scans, depends on your application type (DSS or OLTP).

Have a nice time,