Well, of course it wouldn't be wise to try to get your sound dialed in at an unsafe volume. But the volume should be at or very close to a level that would make the speaker work a little, and generally this will always be waaay too loud for any "bedroom level" playing.
I learned this from a reputable source who has far more experience than I.
Three things to help find this is a flashlight, a friend, and over-the-ears hearing protection for both you and friend.
-Set your amp Bass Mid Treble straight up at wherever halfway is on your particular amp.
-Turn Pres all down, and Master Volume all down.
-Set the OD Gain up about halfway and
get that ear protection on both of you.
-Your friend plugs in and just chugs the low string on your axe. Nothing fancy, no fast thrash triplets, just a steady chug...chug...chug...
While he's doing that, shine the flashlight through the grille cloth on your cab and observe the speaker's movement while slowly raising the Master Volume. Once you see the speaker actually doing something, stop raising the volume. Guitar speakers don't have nearly the amount of cone excursion of bass speakers or subwoofers, so you won't see it really moving a lot. What you will see is that it will appear to look a bit blurry on those chugs and now the speaker(s) are doing their work. Remember, you can always turn it down a little bit from here if you feel it needs to be, but turning it up louder shouldn't ever be necessary.
Adjust the Bass control now just to the point where you can feel and hear the actual cab itself resonating on those chugs.
The Master Volume and Bass is set, and your mate is really annoying you now with those chugs, so take your axe away from him and have him go get beer.
Now see about bringing the rest of your amp and OD level up to speed while leaving the Master Volume set right where you left it. Bring the OD level up as far you want, but if you want some clarity left you may want to roll that back just a bit. Should be easy enough to set your Mid Treb and Pres EQ from there, but those high frequencies in the Treble and Pres can be troublesome, more so in the Pres. area. Leave the Pres. until last after you're satisfied with the OD level, Mid and Treb. You shouldn't need a lot of Pres, since all the "cut" and "punch" in the guitar is lower frequencies than the "fizz" and "sizzle" (and "air" in Clean guitars) that the Pres. control handles. If it seems like you're getting "lost in the mix" bring the Mids up some. Make a note of where your settings are so that after this, you can just dial those settings in and be done with only very minor tweaks if needed.
Something to also consider is the actual speaker placement. Guitar speakers are very directional or "beamy" meaning that they project the sound straight out away from them with very little side dispersion. Because of this, it's easy to overdo the Pres. settings depending on where you are listening from. Save the hassle and adjust the Pres. while listening straight inline of the speaker. This is where the mic will be placed to project the sound through the PA as well, so it makes sense to get it right "here" instead of trying to get it correct from "over there". It will sound a less brighter from "over there" but you'll get used to that after knowing it's set correctly
right where it needs to be set correctly. The ear protection will hinder the settings, (as you do need to preserve your hearing!) so you could let someone plug in while you step way back away from the speakers while staying inline with them to make the final determination.
As always, YMMV and your tone is Your Tone. I learned this from a reputable source who has far more experience than I. We can have the exact same guitar, same amp, same speakers, and play the exact same songs or genre; won't mean we'll arrive with exactly the same settings. But this will get you closer to a good live sound than by blindly Bass +12 Mid -12 Treb +12 the controls