It depends on your room setup and personal preferences. But in general, set the levels so the surround speakers are balanced compared to the sound bar when playing music and TV audio.

It is handy to have your Sonos store the two sets, one for TV and one for music as you often find you like them set differently and being automatic is less aggravation than tweaking them every time.

I tend to set my surround levels a bit higher for TV than audio BUT I also have the surrounds set to Full versus the default Ambient mode so I get a lot more sound from them when playing music.

As said, your ears, your settings.

Pick a TV program with reasonable surround sounds and fiddle witht eh settings until things sound natural from your seating position.

Music settings you need to try twice, once in Ambient mode where the surrounds only carry a portion of what the left and right channels are playing and again in Full mode where they duplicate the left and right channels. Decide which mode you prefer and tweak the levels to make your ears happy.

Do keep Full mode in mind if you have a party, it gets you a lot more room-filling sound without any too-loud spots.