sound engineering??? help

pls help. my band is comprised of electric drums, keyboard, electric guitar, bass and 2 mics. ive got everything hooked to 2 loudspeakers through a 8 channel mixer and the guitar is ran into a multi fx pedal then to the mixer. this rig is so much better than what we've used before but is still relatively new to me. ive been messing around with EQ's and volumes while with the band but it fucks up the flow of practice completely. when we're playing someones always too quiet or too loud and the guitar will be ringing out too sharp. how the hell do set this all up so theres less faff. how loud should each instrument be to blend properly and so we all dont go deaf???