#1
My band and I are clueless when it comes to our PA system. Our guitarist bought a decent used Yamaha PA system (6 input, 250 watts) from a pretty well established local band. This band played live shows with the PA we have now, so it definitely can handle what we need. We're too poor to buy a new one...

Anyway, what should we do for vocal settings and effects? I know absolutely nothing about settings for vocals and since it's not my PA, I don't really tinker with it. Currently, we're getting pretty good volume and it sounds OK at best.

http://www.youtube.com/watch?v=3RGFsG-m2VU

Check out the vocals around :22 in this song. That's sorta the general rock and roll (punk ish) style we're going for. I know that you can do infinitely more to vocals in the studio, but these bands all sound awesome live... what to do?
#2
PA settings will change with whatever environment you're playing in at the time; how certain frequencies bounce around, or get absorbed by, the room and what's in it; what microphones you're using; who has a sore throat that day and so on. So it's pretty difficult for me to sit here and tell you where your knobs should be, if you know what I mean.

So really your best bet is just experimentation. If vocals sound too muddy, take some bass out of the EQ. If they sound too smooth and you want a little more grit, add a little more treble.