Walk through it while they are dancing.

Teach them to promenade first then start dancing

"Promenade anywhere all over the floor
Find two more and circle four"

if they don't manage that, then say "join hands with another couple and move to the left" and keep the music going

"Turn and face your partner, give her your left hand
walk all the way around her and give your right hand to the other girl"

"Okay! keep going! back to your partner with a left, all the way 'round, now the other girl, That's your corner girl, with a right"

"That's it you've got it

Partner by the left with a left hand 'round
Corner by the right with a right hand 'round

Now circle left and don't be late
find four more and circle eight."

Now you have got them in a square, you can stop the music and teach them Sally Goodin using circle left and right as a break.