If the value for Avg Blks/Rd is higher than 1, this indicates full table scans. If it grows higher than DB_FILE_MULTIBLOCK_READ_COUNT we must assume that almost every operation on this TS is executed as full table scan instead of using an index first, so you should consider creating appropriate indices or, maybe, increasing the DB_FILE_MULTIBLOCK_READ_COUNT.

Note that increasing the DB_FILE_MULTIBLOCK_READ_COUNT may have some side effects on the optimizer: it may then prefer a full table scan in some cases you may not like it. Having proper indexes on the other side can never hurt, so I'ld suggest starting at that point.