Micing a choir can be a challenging task. The following excellent videos will walk you through basic concepts of choir micing. The videos are from Audix, and excellent source for choir mics, but other manufacturers produce great mics as well. 

How to Mic a Choir Part One – Introduction and Microphone Choices

How to Mic a Choir Part Two – Microphone Placement

How to Mic a Choir Part Three – More About Microphones

How to Mic a Choir Part Four – More Complex Choir Configurations

How to Mic a Choir Part Five – Setting Up Your Choir

How to Mic a Choir Part Six – Audix Microboom and Final Review.