As a rule of thumb the area between 2.5 - 3.5 kHz is the part of the vocal that gives it legibility. Where in that area depends a bit on the voice. But panning is the easiest way to make room, as Guido said. Keeping the vocal and the main vocal effects dead center and moving the other parts out a little bit. Doesn't need to be all the way. From about 20% panning on the guitars will make a huge difference. Then you can throw a delay or reverb to the other side to compensate "the mix leaning to one side or the other". Pan the acoustic about 20% left, the electric 20% right and the reverse for each instruments reverb/delay. Then you can automate the amount of pan between verse and chorus to make the chorus feel wider, if you want that effect.
Otherwise it's all about carving out space, with relatively smooth moves, usually nothing more than +-3db is needed. I would usually start by giving the electric guitar 120hz & 1.5 kHz, the acoustic 400 hz & the top end (4 kHz and above) and the vocal 250 hz, 600 hz & 3khz and above (for air). Low & hipass anything that isn't needed. I recommend cutting before boosting.
Other tools to make parts stand out and reduce masking is using different styles of compression, the brains is pretty good at separating transients but really bad at sustains. You'll notice this if you cut off the start of a sound and play it back, gets really hard to tell if it is a guitar, piano or some other string instrument. So by enhancing the transients you can make the instruments stand out while still blending.