What are the rules to writing an ode?

Like so many things, the formal definition of an ode has
changed over the years.  One thing that is still the same is the tone and style of this
kind of poem; it is meant to be formal and dignified and is often written for a specific
person or occasion.  A funereal event would often be an occasion for an ode.  In today's
less formal world, this form is often used in parody--using that formal, dignified tone
to honor something more ridiculous or inane.  "Ode to a Broken Fingernail" or "An Ode to
My Rusted-out Chevy" would be examples of this kind of parody. It is the contrast
between a formal tone and style for something which is anything but formal which creates
the irony of parody.

Another element of an ode, in addition
to the formal tone, is a formal structure.  As mentioned above, the form was quite
precise and uniform.  Today, what usually matters is that there is some structure and
some rhyme scheme.  An ode must have a metrical and rhyming
pattern. 

Aside from these two criterion, an ode is
generally what you choose to make it.