Well....it depends on the event. The typical concert (on the road)...
{BEFORE PERFORMERS ARE PRESENT}
1. Turn everything ON (it's amazing how often this is missed)
2. Check all routing is correct w/CD
3. Check monitors/mains are working w/CD
4. Check mics are working
{WITH PERFORMERS}
5. Instruments Only - rough mix
house/band (skip if no band)
6. Vocals & Instruments
That's a rough outline - i'm sure i missed something somewhere