1) Gain structure
2) Gain structure
3) More gain structure

First you need to make sure your inputs are actually at the right level on the board. If it has a gain or trim control and an LED ladder/solo button - push it, and pull the gain up while someone plays/sings until the LEDs get close to jumping up to 0dB.

Start with each individual monitor send set to about the same value. Then bring up the monitor master until it's loud enough, and tweak balance as necessary.

Many bassists feel "buried onstage" for the simple reason that the waveform coming outta the amp takes a few feet (or more) to develop, so you may not hear the amp well at a close proximity. Plus, many of your (ahem) cheaper PA monitor speakers are not really designed for the bass guitar to be pumped through them. They don't reproduce low end well, they are usually designed to project vocal ranges, so I wouldnt "max out" the bass's channel going to the wedges. It may be very counter-productive.
As far as a "process" is concerned, stage monitors usually have the biggest stress on the vocals, so I ALWAYS start with getting the vocal mics as loud as possible (within reason), first by gain staging (per Codechimp), then backing off the master send some so you have some headroom for later in the evening as the singers' lungs get tired and their ears atart to go numb. Your biggest issue is (probably) feedback, at least that's usually the issue. You need to be sure that you have GOOD vocal mics (Shure SM58, Sennheiser E835, Audix OM6, etc) and that the monitors are firing at the "null" spots on the mics' pick-up patterns. This where the mic is LEAST sensitive. Don't know where that null spot is? Check the mic specs on the manufacturer's website. To get you off on the right foot, a Shure SM58 is a cardioid pattern, the null spot is pretty much directly opposite the end that you sing into. Some mics are "hyper-cardioid", and their patterns are the least sensitive at the rear-sides of the mic, maybe at 45 degrees. Position your stage wedges so that the monitors are firing at these points, certainly not at the "hot spot" of the mics.
Start with getting the vocals up to where you need them FIRST, then you can start to add the players SLOWLY and carefully. Don't try to force all of the instruments into the stage mix, your speakers probably won't handle that. If you have a graphic EQ, don't boost ANY of the bands, pull down the very lowest ones, plus some of the junk at around 200Hz. That'll get ya started...

Let me first ask about gain structure. Is this the same as gain unity? I’ve read about gain unity and after reading about it it strikes me there are two schools of thought around setting gain for live performances. The first would be to max the gain at each point in the signal chain (by max I mean turning it up until there’s some clipping and then backing it off a bit). Then use the faders to balance everything out. To moonbaby’s point, starting with the vocal makes sense. The second way would be to put all the faders at 0, do a rough balance by adjusting the gain, and use the sliders minimally to tweek the mix. When I’ve experimented with this the gain’s aren’t typically any where near being maxed out for each channel.

So, in one scenario the first step is to start with the gain levels. In the second, you first set the fader levels (at 0).

Is this observation right or am I missing something?

Oh, just a bit more info. The band is a bluegrass band and I play standup bass - not bass guitar. I don’t know that this makes a difference but I thought I’d put it out there.

I think the idea of starting with the vocals make good sense. That is the most important part of the music.

It's essentially the same thing. People have variations - gear can be used in different ways - for example I run everything a little UNDER what is recommended because the preamps won't provide enough gain and it leaves headroom for people getting excitable with mics.

How are you inputting the bass? At some point I would run -only- the bass through the monitor and turn it up to see what the signal sounds like, and if it's loud enough. Could be that the signal is poor, or mostly bleed from other instruments which makes it harder to mix.

I'm use a Fishman Pro-EQ Platinum preamp/di. I've got a good strong signal.

I started this thread because somehow everyone in the band got turned up (a little more banjo, a little more guitar) that there was no more room for me (so sad!).

I'm thinking that maybe this is easier than I thought. Following up on Moonbaby's comment, I'm thinking I should first set the vocals at maybe 1 O'clock to give me room to tweek. Then, balance everything else with the vocals. I'm thinking that if the gains are properly set then the signal strength of all the instruments should be about the same. Theoretically, I should even be close to maxing out any instrument (I think/hope).

Does this make sense?

Yeah; no maxing out should be required.

This should be the case, but for 1 thing...

You set gains based on the peaks as indicated by a bunch of LEDs. What comes out the monitor is entirely different than peaks.

On top of that, the frequency ranges will overlap and cause mush, the way the monitor affects the sound will, umm, affect the sound too.

So yes; they will be similar in strength but don't expect to be able to set everything to 2oclock and have a perfect mix.

I completely get that Codemonkey. I was just suggesting starting at 2:00. I picked 2:00 as I thought it would give me ample room to adjust up or down without hitting any extreme limits (which was my original issue).

When I'm dealing with a situation where there is only one monitor mix, I like to keep the bass and keys very low or out if possible. Give them their own small amps on stage to use as personal monitors. These amps don't need a lot of low end and should be pointed at the players ears. I've used a little Peavey micro bass practice amp as a personal bass monitor and as a monitor for keys. No, it is not a sound that is particularly great, but it gives me a clear idea of pitch and it does not add a lot of mud to the stage sound. (The goal of a concert is to give a good sound to the people in the audience - not the people on stage.)

This is a thread near and dear.. as I struggled for years trying to get a good on stage sound mix.. as there were always complaints (usually from the bass player) that they couldn't hear themselves.. or my favorite stage mix where the sound literally bounces around and everything sounds disconnected - like it's out of phase!

I'm not the sound guy (just the drummer), but I will say the best sound guy and sound I ever got went something like this;
- first thing he did was turn off the FOH speakers and asked us to setup and play like we were in our practice room. So, first just just backline amps and then the monitor mix. He had a wireless tablet with a pen, and he walked around the stage and tweaked the levels on the tablet. After we were all happy with the sound balance, he walked to the back of the arena and using the tablet brought up the FOH speakers and tweaked some more. The sound was awesome.. and it made playing that much easier!

I don't even WANT to know how expensive that would be.

*thinks regardless*

Digital mixer, PC with bluetooth, tablet has bluetooth connection, mixer connected to PC and with software that can control the mixer running on it.
Connect to the PC via SSH/VPN/RDP or something, and hey presto. All you need is a wireless tablet and an externally controllable digital mixer (via MIDI or USB or something) which I think is 99% of them?

Unless he created some sort of wireless device that transfers MIDI information to a mixer...
*stops thinking*

Also, can I point out that it's ALWAYS ALWAYS ALWAYS the bass player who can't hear themselves enough!!?
Do bass players have desensitised hearing below 100Hz or something?

Bluegrass is particularly tough when there arent onstage amps for personal monitors of the instruments.

Especially for the bass. You need an onstage amp. There is no other way around it.

Gainstaging a live show isnt so much as unity gainstaging as you might think. Understand that the gain control on the frontend of each channel also sends the gain to the monitor bus, the effects bus and anything else you might have going out of the master section. Looking at it as 'all things being equal' is a falacy since they really arent. You set each channel to match the input level of the individual instrument....some will have more gain than others and will also have more swing in their ability to add gain during 'exciting' moments. Other instruments will keep a fairly level input and once they are set will retain their continuity throughout the performance. Vocals, are not one of those.

You set the vocal mix for the stage level first and foremost. The rest, especially with a bluegrass band, is filler.