Originally Posted by: axemaster911Considering the volume levels at some of our sessions sign language may be needed. ( joking )
I see what you mean. What keys work best together, and what keys dont? Is this a trial and error technique, or are there common set guidelines for study?

There are guidelines. Many, many guidelines. Pick up a good theory book on modulation and learn a few (if you plan on doing this with a band, have them learn the guidelines as well). I wouldn't say two keys work "best" together... Really you can modulate to any key from any other key. Though for quick modulations, the relative major/minor, the dominant, and the parallel major/minor are pretty simple.