I usually set my tone to -20db. Then I set my audio peaks to max -6db. Usually, my dialogues, are ranging inbetween -12db to -20db. As for background music, I put it in the sequence with the dialogues and play with the audio level so that the dialogue will be around -20 to -12db and that the background music doesn’t interfere with the dialogues.
In the end, as long as the audio levels are technically respected, it’s your ears that will set the proper balance…
Hope this helps! 🙂