Start with volume and tone all the way open. Balance in the middle. Then set your amp to produce sound at a volume and tone that you like.
Roll back the tone if your sound is too bright and you can't deal with it at the amp first.
Use the volume to - well I'm not sure about that one. Turn it down all the way if you want to take a beak and put the bass on its stand. Some people play with volume lower than 100%, but I don't feel good about introducing extra resistance into the signal path and lowering the first element of the gain staging chain that begins at the bass.
The balance is very subjective. The overall timbre and balance of the tone should change radically from one extreme to the other. I'm a fan of keeping it in the middle and plucking the strings at different positions to get different tone. Plus, the middle should be easy to find with a detent.
Best advice there is to do whatever sounds good to you.