The key to a good in ear mix is to first realize what you don't need in your mix. For example:
Some of the places I play at are very big rooms. Ambience mics in those rooms give big delays, which mess up my timing. No ambience mics. Similarly, there are often many (6 to 8 vocalists) on stage. If someone isn't singing lead on one of the tunes, they are off in my mix. This usually means there are 3 or 4 vocal mics on in my mix - that's plenty, and limiting the vocal mics that are on limits ambience (again, echoes and such) that comes in that way. A lot of vocalists like reverb on their voice - makes them feel less naked so they can singe better. Although they don't sound as good without it, that's off in my mix.
Drums - I do need to hear kick and snare well, but it doesn't all have to come in via my ears. There's usually some bleed from the drums themselves, and I add just enough in my mix to nail my timing. There's also some overheads in my mix, but I don't need a lot of the other spot mics, so they stay off.
Guitars, keys. A lot of the time I'm playing with an acoustic, 2 electrics and 2 keys players (usually piano and a B3). That's a lot of stuff. and hearing it all well isn't going to get me what I need.
What I do need is to know where I am in the arrangement, and have timing and pitch cues, to make sure i'm playing the right thing at the right time.
To that end, my mix has these things in it (from loudest to quietest);
1) Me. I m responsible for my part, gotta hear it.
2) (About as loud as me) - the lead singer. My job is support whatever he or she is doing, and if I can't hear him or her, that's a problem
3) Drums - kick, snare, some overhead. No effects on anything
4) Whatever instrument is best at giving me pitch cues - typically that's the piano keys player - that's more rhythmic and has more usable pitch information than the B3
5) The other guitars and the B3 are below this, those have to all be kept fairly low, so they don't step on the primary stuff
6) backup vocalists - usually off. There are some gigs where they aren't a lot of singers, and maybe I'll sneak some of those in, but I don't do that unless everything else is comfortably there, and there's room left for them.
The point is, everything in my mix is there for a reason - if something helps me do my job better , it's in my mix. If not, I get rid of it. My mix is not something that the audience would love to hear, but the result of it (that the band sounds better because I have the right information to do my job well) is something they hopefully do appreciate, even if they have no idea where all that came from.
Oh yeah, that topic. I find that NOT having an amp on stage is a huge help. Yes, it's fun to be flapping your pants with low end, but the bleed into my ears, and also into the audience makes everything messier and less precise. i like a dry mix that has just what I need, without anything to that gets in the way.