If you have access to MOS Notes then please see the MOS notes below, I have found these very useful.
Some of the topics covered include compression master notes, critical compression patches, Data Guard Redo Transport Compression, index key (prefix) compression, IOT compression, DataPump data compression, compression advisor, Hybrid Columnar Compression and more.
Advanced Compression Master Note (Doc ID 1223705.1)
How to compress a table that is online (Doc ID 1353967.1)
Advanced Compression critical patches (Doc ID 1061366.1)
Redo Transport compression with Data Guard (Doc ID 729551.1)
How to see if rows are compressed in a table (Doc ID 1477918.1)
A complete understanding of RMAN compression (Doc ID 563427.1)
How to determine if Advanced Compression is used by DataPump (Doc ID 1993134.1)
Index Organized Tables (IOTs) and compression (Doc ID 1555637.1)
How to find the optimal Index Key COMPRESS level for Indexes (Doc ID 601690.1)
Advanced Compression Restriction on 255 Columns Lifted For Oracle 12c (Doc ID 1612095.1)
How Does Compression Advisor Work? (Doc ID 1284972.1)
Exadata Hybrid Columnar Compression (EHCC) FAQ (Doc ID 1910687.1)
Also, if you are attending the Croatian Oracle User Group (HrOUG) meeting in Rovinj in October, please stop by my sessions on Database Compression Best Practices and Flashback Data Archive
Using Oracle Flashback Data Archive to Track and Store Transactional Changes
Thursday, October 17, 2:30 p.m. – 3:15 p.m. Hall A
Compression Usage Insights – Getting the Best Out of Oracle Compression
Thursday, October 17, 4:30 p.m. – 5:30 p.m. Hall D
See the HrOUG Agenda here!