Another cool technique is Blumlein.

Where two Bi-directional microphone are one above the other with the two microphone capsules as close together as possible. they tend to be placed one on top of the other vertically.

the two capsules are perpendicular to each other (90 degrees) and the sound source is placed in the mid point of the two microphones.

check out some photos on google for an idea of how to set it up