How to properly configure spam filtering?

Question

Debian

Hello.
Interested in fine-tuning SA or SIEVE. At the moment, SA is trained and does its job well, only 5% of spam passes per day. But I would like to reduce this figure.
For the most part, spam passes, where the recipient's address is indicated in the blind copy (BCC).
What should be configured in this case? SA or set up conditions in sieve (tell me which ones, because I'm suffering for 2 days, nothing comes out)?