Calligraphy means beautiful writing and in a conworld, —if you are using a conlang— this must fit the language it is being used for.
For example, if the language uses glyphs like
= Λ < · \ v
we could (although a bit confusing) decorate to become
Ξ A c o λ U
≤ /\ © . δ
which could make glyphs easy to confuse. Calligraphy is usually written with an instrument different from the one normally used for writing so thinking about which instrument that was could make an idea of how to write. A method for making up a calligraphy for a conlang could be to highlight the differences between instruments used for writing normally and those for writing calligraphy (can you draw straight lines?, and curves?, do you use colours?...) or they may be based on con-aesthetics (aesthetics are a branch of philosophy which studies the concepts of beauty and art). In some cases it could also be based on drawings of things which remind about the glyphs avoiding something too similar to other glyphs.
It could be applied to con-literature.