I remember that I used a table from Bobby Owsinski's handbook. Luckily that table is online now:
Examples why it depends on the song:
You have two tracks of guitars playing (almost) the same: you can pan them hard left and right.
The song sounds good with a scooped out guitar sounds: shouldn't be a problem with vocals.
The acoustic guitar strums but there are other instruments to identify the chords: that guitar could be used more as a rhythmic instrument.
The acoustic guitar is picking patterns and it's the only instrument: now there could be a problem.
Do you have a little excerpt from your music to listen to?