I would mostly listen to your ear and what YOU like. My general philosophy, personally, for each individual knob is:
Bass- add enough to make your tone thicker and bigger, but not so much that it sounds “flubby” and not tight. Some amps have so much bass by nature that I can only turn the bass up to 2 like the Bogner Uberschall that Syn used for years, or a Mesa Mark V, or the Rivera Knucklehead Tre. All SUPER bassy amps.
Mids- Keep these pretty high, too low and you disappear in the “sonic spectrum”, especially when playing with a band. Scooped mids is fine in your bedroom, but the more volume and instruments you, generally the harder it is to hear you. Its also not the best for singing leads. You also dont want it so high that it sounds “right in your face” Mine generally stay above 5 and below 9.
Treble- the guitars voice sits in the higher register than a vocalist and the bass so you definitely want some highs, but you dont want it to be “ice picky” and stabbing people in the ears. Mine generally says around the 7-8 range depending on the amp. Some amps also have a “presence” knob and these are the REALLY high highs. Its treble, but a different frequency. I usually like to take it easy on this and keep it around 3 and almost always under 7. You can kind of shape you high end tone by balancing these two. Play with that balance a bit.
Gain- This depends on musically what you are going for. For cleans, you obviously dont wanna crank that too much. Sometimes you just want a little breakup for like blues or lighter rock passages, so you turn the gain up a little bit. You can also have a high gain sound and turn the volume knob down on your guitar to get this sound. This is also how guys had to get a clean sound back in the days of amps only having 1 channel. They would set the amp up for the highest amount of gain they needed and back the volume off on their guitars to clean it up. I think Zakk Wylde still does this. When you are going for a metal or lead tone, just natural feeling is to crank that bad boy up to 10 but I would generally advise against that. You wanna turn it up to get a singing tone or to get that chunky rhythm sound. You definitely want it up enough so it doesnt feel like you’re fighting your amp to make notes come out. you also dont want it up so high that you get a big garble of sound coming out. This is a mistake a lot of newer guitarists make. The older I get the more I seem to back off the gain, and I get a heavier and bigger sound than I ever have. Too much gain can be your biggest enemy.
But always remember: USE YOUR EAR! It’s YOUR sound!