diki,
as always, your answer is helpful and it pretty much confirm what i think too. actually, i tried this idea (putting the volume down all the way and then slowly rising it) and it does work! it gives a good idea about how loud the vocal is compared with the rest of the tracks.
now, what i am really interested in is also how the other tracks are related to eachother...
so, if vocal is 100%, let's say already processed, then, what is bass? (80-90%?) and what is bass drum? then the snare... then the hihats... then guitars, etc.

i very well understand how tricky all this is, and how dificult would be to give a right value without actually mixing a certain song, but for me is very important to have like a starting point. i tried many aproaches, and it seams that always something is too loud or too quiet, and the balance (volume levels) are somehow... unbalanced.
i am curious, raughly, what would be a good starting point...
what si your aproach on this?
and thanks for the answers, diki, i apreciate!