by Jessi edited by Melissa and others
(23 Anthesterion) Appeasement festival in honor of Zeus Meilikhios (kindly), which took place in the countryside to welcome spring with solemn but joyful celebrations and honor also the chthonic aspect of Zeus. There were night rites with sheep or pig-shaped bread or pastry offerings, sacrifices, feasting, dances and hymn chanting (Parke, pp 120-22).
To celebrate in modern times: As this was a more rustic and family-oriented festival, it is a good time to spend with family and friends. Hold a feast that includes bread, ideally in the shapes of sacrificial animals. Remember the dead on this night as well as the well-being of your family (however you view it) with offerings and libations.
Parke, H.W., Festivals of the Athenians, 1977
A sample ritual can be found here.