I think the easiest way to start calling squares is to do phrased
New Engand style squares, as they feel the most like contras.
You can take risks with breaks, however, that will then lead you on
the path to calling unphrased squares. The trick here is to be very
familiar with dance music (and especially old time if that's what you
want to call squares to). Even for unphrased squares, you have to know
where the musical phrase is. Breaks are great because you can mix up the
figures and use a partner swing to take up the time and get you back on the
musical phrase.
Tom Hinds, Tony Parkes and Gene Hubert have all written exciting, phrased
sqaures.
Lisa