Since: Dec 04, 2007
Short answer, the starting EQ should be flat. xD
I'd say there really isn't a "standard" setting. All voices are unique, and all voices will have certain frequencies emphasized just by the nature of the singer's genetics (shape of vocal chords, lung capacity, fitness, etc.) and how the mic response (along with the room/stage) emphasizes the vocal source.
Use your ears to get a feel for how the untreated vocal track sounds, and ask yourself if it sounds muddy, or sibilant, or harsh, or whatever. Think about what frequencies exhibit those qualities, and use an EQ to zone in on the problem areas.
You could get a parametric EQ, create a notch of about +10db, sweep it, and find the ranges where the problems come out the most, then, using your ears to judge, cut where and how much your ears tell you is appropriate. If it sounds a bit dull after cutting the problems out, then maybe add back a little presence somewhere in the 3 to 5khz.
Or, with the 31-band, lower the fader a bit (3 or 4 db?) in the ballpark where you think the problem is occurring. If it sounds better, leave it. if it sounds worse, move it back to flat, and listen again, and try to figure out where the problem is occurring.
Just be careful when cutting and boosting. If you cut or boost too much, it's easy to get a vocal to sound unnatural.
Also, is this in a recording situation, or a live PA/stage situation? If it's a live situation, I'd use the 31-band to tune out problems in room and feedback. Then use the mixer EQ to adjust vocals if absolutely needed. If it's recording, then yeah, what I said above should help.