Depends on the model. On my MicroPro I turn master all the way and adjust the gain to taste. +plus the limiter to keep it from getting too gainy if necessary.
I agree with Stew. With volume pedal wide open, turn the gain up till the amp starts to distort, then roll it back a hair. That allows you to run the master V as high as you want without breakup.
If you are running it fairly clean, I would just leave the limiter off.