Using the volume displays lets you see visual cues in the waveform for aligning the volume (or other parameter) at exact places and levels in the audio. A typical adjustment would be to drag a music bed down, often about 12-15dB, under a voice.
Start the duck before the voice-over, then continue fading a bit under the start of the voice — this makes the transition smooth. A straight-line linear drop in volume often sounds a bit mechanical, so add more breakpoints, then create a curved, more natural sounding duck. The “best” shape of the volume change depends on audio material and personal taste, but often, gentler curves sound better.
Don’t be afraid to make long, gradual adjustments over many seconds, even minutes — i.e., not just for short ducks or boosts. You can adjust the volume automation of any track, including aux channels and master faders. Making volume adjustments to those grouped channels can be a real time-saver.
Selecting a range of breakpoints lets you delete them (with the delete key). With the Trimmer tool, you can select, then drag multiple breakpoints up or down to raise or lower them all, while preserving their volume shape.
When you move or delete audio regions, their automation data should move with them. Unfortunately automation may glitch during large structure changes. So it’s generally more efficient to only make rough level adjustments at first. Then, once you’re more confident of the placement of all your regions, go in and do the fine adjustments.
After you make a volume change, listen to it. Fine-tune the breakpoints for a mix that sounds good to you.