I'm late to the party but, it really depends on the gig, the size of the room, the monitor situation, etc.
If I'm using a wedge, I get a smattering of all the other instruments, and - no matter what - I always make sure to be able to hear the front end of the bass player's notes. Even when they aren't my rhythmic ally, so to speak. Other instruments are balanced depending on whether they're a help or a hindrance and how much of their sound I'm already getting on stage. If it's a gig with an MD, I always have plenty of whatever they're playing in there because in the end I have to follow them wherever they may go. Well, at least until I've been on the gig long enough to ignore them.
On a pop gig (I include jazz singers in this, BTW) I want some vox because I want to hear the melody and the words so I know what the heck is going on. The level depends on how good the singer is and whether or not they're my rhythmic ally or not. In musical theatre situations I tend not to get much vocal because often times they're going to be a bit loose about rhythm. They're acting as much as singing with a band, so I let the conductor/MD worry about tempo and ignore what they're doing up on stage for the most part. This problem is magnified with ensemble/chorus numbers. Big choruses/choirs almost always drag.
In a really big venue, I might put some bass drum and snare drum in my monitor but I don't tend to like too much of myself. I only get it when it's likely that my own sound will get lost and I'll end up whacking the hell out of the things just to hear myself.
With IEMs it's all different. It really depends on the situation, but my basic MO is to get a mix that helps me keep time and support the music the best I can. If it's a gig that's on click/track, then I'm going to have a lot of that in my cans because in the end, a lot of the time, the other players are going to play to me as much as the click. Moreover, I'm the click for anyone else on stage without one - i.e. actors, singers, dancers, etc. Tracks are great, especially percussion tracks and if I've got those, I'll usually be swimming in them as I find it really helps me relax and not feel I have to fill space and propel the time on my own.
Personally I don't love IEMs because they bring me out of touch with my own instrument. But, they're part of the game now.