FOH (front of house)levels are difficult to judge from stage, so if you can't have the luxury of a sound engineer, you need to let some kind of "demo" program play while you go out and listen to the mains.
In most smaller situations, a reasonable level can be mixed from stage, but it really is VERY important that the sound ON stage is acceptable to the performer first. You NEED to hear the product you are trying to "sell" or else you won't be able to perform it to the fullest.
Most of my work is not in larger venues, but when it is - i am usually in front of the main, so I hear the full mix that way... as well as my vocal monitor.
Another rule of thumb, for me is this -
I always make the crowd tell me to turn it UP before they tell me to turn it down. Psychologically - it makes a better first impression. Makes me the hero early on.
Must run.....it's almost time for the SUPERBOWL (at least to NY & Philly fans !!!)
Hey DanO - tough loss yesterday ..... hope your Ravens beat up those Bucks a little so they're tired next week!