I've done some of that. No "big" gigs though, the biggest one was a gig in my jazzclub with the (most) famous swedish guitarist Janne Schaffer. I got compliments from him about the sound so I'm happy about that.
Some tips:
- Don't overdo things. Use what's appropriate for the venue. Everything don't need to be miced in a small/medium sized place. Use a minimum of effects and dynamics processors. I'm not saying you should shy away from them, just use them sparsely.
- Always listen to and look at the band playing. Make sure everyone is heard in the band and the balance between instruments is good.
- If the band features vocals, make sure they're heard. If not, cut the other instruments down. As a general principle, don't boost the bass on the vocal mic, as it usually only makes the sound blurry and undefined in the mix.
- Learn how to use the mixer and how to set the input gain knobs properly. Take the time to learn how all frequencies sound to be able to use the eq more effectively. Learn to use the other parts of the system as well. Read the manuals. Experiment.
- As with bass, boosting mids is a good way to make an(y) instrument cut through better in the mix. Boosting the volume might just make things blurry, e.g. if you have to deal with a scooped heavy-metal guitar sound.
- Bass drums sounds the best (very IMO and jazz being an exception) with the low mids cut down rather heavily and some high mids / treble is boosted slightly. Eliminates feedback problems as well.
- Lighting cause problems in the form of humming if they're put in the same electricity phase and a dimmer is used. Always put sound and lighting in different electric phases whenever possible.
I could go on, but here's a few tips to get you started. Anyway, since I know what you've told us here on TB in other threads, I'm a bit concerned about your hearing and how it would affect the mixing. You will mix according to what you hear, and if you have some serious issues with your hearing I'd advice you against doing to much mixing. Do you have a graph of your hearing? I know I have a cut in the high mids at about 4 khz but I don't consider it significant enough to have a major impact on my mixing abilities.
It might be stupid, but I don't like to use ear protection when mixing a gig. Most people in the audience don't wear ear plugs either, and I don't like to fool myself with a weaker and possibly morphed sound. This way I'm keeping the volume reasonable for everyone, and I hear exactly what the audience hear, which is a good thing IMO.