It really depends on the type of gigs that you are playing. If you are playing on a relatively small stage, you should be able to hear the guitar with little to none in the monitors. If you are on a bigger stage and the different players are spread out more, you might want some guitar in the monitors.
As far as vocals go, I always like to put all vocals in the monitors. It helps to solve two problems. The first thing is that it helps everyone because they can hear themselves. The second thing is that putting all the vocals in the monitor mix is a big help when it comes to harmonies. This allows the vocalists to tell if they are in tune with each other, thus producing a more pleasing sound to the ears for the audience. Hope this helps.
-Matt
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"Give a man a fish, and he'll eat for a day. Teach a man how to fish, and he'll spend all day in a boat drinking beer."
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