Hi,
I would like to contribute some code in the near future and haven't found any suggested procedure to submit it ... or have just overread it.
What is the best way to do so?

Kind of depends on what sort of code you want to contribute.

New features for zenphoto are best done as plugins. If you make a new plugin let us know and we will add it to the page of contributed extensions.

If the code fixes or enhances the zenphoto core you should create a ticket describing what you are doing and attach the code to the ticket. (Actually, you can use a ticket to let everyone know of a new plugin as well.)

If you are planning on modifying the zenphoto core, you should be using the latest SVN/Trunk build so that your changes will integrate well into the current development stream.