Hello. my question is. how to setup the whole band sound so that it sounds good? what things are important to be careful? how to setup the singer...? my band allways has troubles. someone is allways too loud, too bassy, to quiet...
There's not really a short answer here and there are a few factors that come into play here.

First, if you're playing a gig where everything is mic'd up and ran through the PA, keep your stage volumes low and let the monitors do their job. The size of the venue and stage will dictate how loud you'll want your volume to be. Personally, I like to have something of a "bubble" of my guitar sound on stage, which in the small-to-medium size venues I routinely play, this is very achievable. I like to have a nice combination of amp volume and my guitar in the monitor so I can move around on my side of the stage and be able to hear myself adequately within the area I'll be on stage. From there, I'll have the sound man run whatever else I need through my monitor.

If you're playing a gig that's unmic'd (or at practice), the best way to get a nice sound setup is to have the drummer start playing and add in instruments from there, setting the volume levels accordingly. A good order to approach this in is drums, then bass, guitars (rhythm first then lead), and then vocals.
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The simplest way is to set up your amps so you get a good balance on stage and simply forget about front of house. Mike up everything and let your sound guy take care of FoH. What I do is employ my own sound guy and pay him 10% of the take. If your singer can't hear himself it's up to him to tell the sound guy so he can put more through the wedges. If you have your own sound guy he will get to know your band and should sort it all out without drama.
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