Placement for recording: Up high, above the conversation, if possible, or close to your ears. (I clip a pair of binaurals to a shirt collar--not ideal, but if the mics were on my ears/eyeglasses the sound would swing around whenever I turned my head.) Any further below shoulder level, though, and you're going to start getting the sound muffled by the audience members in the way.
For placement in the room, my advice is: Get there early and (assuming you're not in reserved seats) walk through the room. Close your eyes and listen to the pre-show music. Is it bassy? Is there an echo or an oddly emphasized frequency range? Can you make out the words in the vocals? An even better time for this test is during the opening act. Close your eyes to take away visual cues, like lip-readiing the lead singer.
Rule of thumb: Stand near the sound booth.
Rule of other thumb: If people are yakking, get the hell away from them.