The last time I was here, I was discussing my frustration concerning past experiences with operating live sound equipment improperly. Just last week, I have bought a First Act two-channel PA amp for around $100. It works really well, and one of its channels is labeled for the vocal mic and the other is for the instrument (guitar, bass, keyboard, etc.) Right now, I am using it for practising my open mic sets, and I hope to use it to play some gigs in the near future. The main thing is that the vocal has to be louder than the instrumentation because that is the source of the melody. Otherwise, nobody will hear or understand what you are singing.
From all of my past experiences with running (or attempting to run) live sound, I realise that I should have been as assertive about it then as I am now because with things like this comes some form of criticism, be it constructive or negative. Still, you learn from what people tell you.
Hey Benji, as far as a hierarchy of sound levels goes, I remember this magic bus parable:
"The basic, most primal part of music is the beat. Its always there. Sometimes, you don't even know its there. Sometimes, it punches through to get you where you have to go. Thats the drums and they equate to the bus's motor. The motor gets you where you want to go. Here is where the bus driver comes in. He keeps the bus on the road and not careening off of a cliff. He also is called bass.
The body of the bus, the part you see from a long way, translates to the vocals. Picture a bus full of kids on a field trip singing their hearts out. You can see and hear them before you could see who was driving or hear the engine. Now the last part is about the kid who hid on the roof with the luggage. Thats lead, and he is screaming his lungs out. You don't notice him until the bus gets close. When the bus goes by, you can't miss him."
So thats a parable about dynamics. Dynamics make good bands into great bands. For the most part, vocals should be the loudest, followed by lead breaks. But, as a disclaimer, there are different ways to do things. Its all about communicating with each other. You should have a dialog going on with yer buds to establish your own dynamic.
These are the reasons we practice, to work that stuff out before you get caught in front of an audience.