What forms do ceilidhs use? (lines? squares? something else?)

Here it's always been that the "head" of the contra line or couple #1 in a square is nearest the band, regardless of where is the front of the room. "Active" couples in contra lines are the ones facing down the set (backs to the band, but at the "band end" of each set of two couples). Couples 2, 3, and 4 are numbered from the right of couple 1 around the square. Genders are just "men" and "women" even if the individuals aren't. Occasionally they're "designated" men and women if a lot of them aren't, otherwise you're just expected to remember that you've had a temporary sex change. We sometimes pass out spare neckties if there are way too many women dancing as men--it just makes things easier when you're trying to find your new "male" partner at a high rate of speed.

If we had a lot of inexperienced dancers, we'd often insist that people change partners with a more experienced couple, at least for a dance or two, so they would have someone to haul them along a the right clip until they had a better feel for it.