They normally start By the right, Across The set, though sometimes as, for example, in bars 49-60 of Seton's Ceilidh Band, the Dancers first Cross on the sides. In a Square set, the 2nd and 4th Place Dancers also start Across The set whereas the 1st and 3rd Place Dancers usually start Up and down.
This Figure takes 4 bars in all, 2 for each Crossing movement with sharp rotations at each corner. The Figure should Finish with a Polite turn whenever practicable. Traditionally, the Polite turn was omitted for those Dancers due to follow the Half right and lefts immediately with a repetition of the Figure from different Places as, for example, the 1st Man and 4th Lady on bar 4 in The Garry Strathspey, where they have to repeat the Figure from 2nd and 3rd Places on bar 5; nowadays, this exception is often ignored.
In a 4-Couple Square set, the path may still be a rectangle but rotated so that the Dancers Cross diagonally both Across The set and on the Sides. 4 Dancers are involved and they Finish Diagonally opposite their Starting Positions.
In a 3-Couple Triangular set, the rectangle becomes a trapezium; this requires a much quicker movement by those Travelling on the longer side of the trapezium. 4 Dancers are involved and they Finish having Exchanged Places. For example, in bars 25-28 of MacPherson's Jig, the Couples in 1st and 3rd Places Exchange places.
See also Rights and lefts halfway diagonally for that specific form.