I know it's standard to add more instruments in the chorus to contrast it with the verses, but what do you do when the instruments in the chorus overpower the vocals? Do you turn up the chorus vocals?
Also, are you suppose to make the volume of the verses and choruses equal even if the chorus has more instruments?
First of all, I personally agree 100% with everybody that has said there is no "supposed to" in mixing your tunes. Go for what sounds cool, conventions be damned.
Still, the above statement doesn't mean that tried-and-true tricks are necessarily a bad thing.
If you have a song where the chorus instruments are "kicking in" and burying the vocals, then you could simply automate your vocal level upwards for the chorus sections. You may need to move the other parts down a bit so that you have enough headroom to do this (i.e. if the verse vox are already maxed, then it won't work).
Personally though, if I'm recording a tune that has clear breaks in the louder/softer parts, I prefer to avoid using automation and just record entirely separate tracks--in your case, this would mean recording your verse vocals on one track, and chorus vocals on a separate track. This way, you can set the levels of the two individually and off you go.
Also, like somebody already mentioned, you can try double-tracking (recording 2 takes of the exact same thing and using them together). You'll find that this really helps cut through the loud backing instruments. If you go with a single vocal track (panned center) for a quiet verse, and then switch to a double-tracked vocal (panned left and right) for the chorus it makes for a nice effect in some cases. It won't sound good in all situations but it's something to try. If the chorus instrumentation is loud enough the double-tracking effect can be almost transparent to the casual listener.