I now wish I'd paid more attention to the speaker who was teaching "copperplate" calligraphy to my guild. She gave several rules for flourishing including never cause three lines to intersect, never push for complete symetry and go for parallel lines (no "almost parallel" lines) and balance filled spaces in a calligraphied piece. She also said to be careful, but do use ligatures, and vary the ascenders and descenders - don't make all of them ornate. Sadly, I was more into the medieval flat nib (blackletter) at the time, and didn't realize how fun and useful Spencerian script was until years later. Sadly, I can't even remember her name!
Here's a book that might help you, if you have some calligraphy background:
Bill Hildebrandt's
Calligraphic Flourishing: A New Approach to an Ancient Art. David R. Godine Publisher, po Box 9103, Lincoln, MA 01773. 1995. xi, 115 pp, illustrated. isbn 1-56792-028-4. It's suppose to be good on technique and methodology of construction.
Dover has a couple of flourishing books, too and look up copperplate calligraphy, penman calligraphy and ornamental calligraphy to find a bunch of others.