One-stop shop for learning standard mic stereo techniques like ORTF, XY, DIN, NOS, Blumlein, binaural, baffled, Decca Tree, Mid/Side (M/S), A-B.
Everything you needed to know about these techniques are at the DPA Microphone University:
http://www.dpamicrophones.comThat said, don't be afraid to adjust these standards depending on the situation at hand - less than ideal room acoustics, crowd noise, physical location, etc. Experiment!
Also:
http://www.oade.com/Tapers_Section/faq-mic.html