Noumenia
Seventh Day of the solar month
"... the Hellenic festival calendar is lunar based. The beginning of each month is marked by the appearance of the new moon. This usually takes place on the day after the astronomical New Moon in any particular region. The first day of the month is named Noumenia and it is a sacred day, dedicated to Apollon. On this day we honor all of the cherished Gods, and especially the Household Gods: Hestia, Apollon, Zeus, Hermes and Hekate."
"A common practice is the cleansing and incensing of the statues and renewal of the offerings on [...] altars and shrines..."
- Hellenic Polytheism: Household Worship - Page 103 (LABRYS)
How to Celebrate
Remove old offerings from all altars and shrines, discarding them in the appropriate manner.
Clean all household altars and shrines, be sure that each statue is cleansed and that all surfaces are free from dust.
If your Okios keeps a Kathiskos, it should be cleaned and replenished with new offerings. More information about the Kathiskos can be found here.
Provide fresh incense, or a comparable offering, to each of the household altars and shrines.
Set time aside to invoke, honor, and pray to each of the household gods and divinities.