Here are eight articles about sound system operation.

One thought that hasn't been mentioned yet: The microphones you will be using are undoubtedly ones that are designed to pick up sound primarily from directly in front of them, so be sure to point them directly at the instruments they are supposed to pick up. The musicians may know this, and adjust the positions of their mikes themselves, but if they leave the mike position up to you, then you will have to point them appropriately.

Jacob