"What works well is if the more experienced dancer takes the less
familiar position. Just position your hands to indicate that you're
ok taking the less customary role, and if the other person is faster
to do so, go with that instead."
Jeff
I'd like to look at this issue as a caller, rather than a dancer:
When calling such a dance we, as callers, should not assume that for every
pairing at least one of the two has danced the other role. "The more
experienced of you should take the less customary role" is not useful
advice to 2 people who just started today.
I dislike the idea of telling the dancers "you figure it out." We should
probably teach a symmetric swing so there can be a default amongst those
dancers who don't yet have a collection of alternate swings and experience
dancing both roles. Dancers with a certain level and type of experience
will, of course, make something up regardless of what we tell them.