The people of Mykonos are for the most part pantheistic. Although they would never be called particularly religious, the gods do play an important part in daily life. Most of them have a healthy respect for the gods and make it a point to make offerings to the gods in hopes of a blessing or favorable outcome. But the gods, for the most part,  don't meddle in the affairs of mortals.

The rich often throw lavish parties or sponsor some sort of entertainment in a god's name as an offering or a celebration of a holy day. Those of lesser means offer other things like sacrificial animals (the flesh is then fed to the poor), recite poems, offer dances or anything else they feel will please the gods. Sincerity and personal value of the offering seem to be more important to the gods than the size or monetary value of the offering.

There are a couple of ways people come to the priesthood. Some families particularly the well off will promise a child to the temples. Other children are god touched and enter the temple to fulfill a vocation. And unwanted and orphaned children are made wards of a temple. Upon reaching their teens, the children are given the choice to take holy vows or to leave the temple and apprentice a trade.

All children are giving the chance at a basic education, which includes reading, writing, math and an explanation of the gods and their spheres of influence. Children who enter the priesthood are further educated, the fields depending on their deity. They are also introduced to the mysteries of their chosen god.

To encourage inter-temple peace, novitiates are encouraged to visit and even take classes at other temple. Sometimes at this point, a novitiate feels the call of a different god and changes deities. While there aren't any outright battles between the gods, there are tensions and god switching after taking final vows is strongly frowned upon.

Once a novitiate has finished zir studies and taken zir final vows, zie may choose to adventure and spread the word of zir chosen deity or stay within the temple precincts. Most priests have responsibilities within the community. For example, Tuath's Loremasters also oversee the schooling of all city children and Galan's priests serve as healers and apothecaries.
 

The Nitty Gritty

Each deity has a portfolio of individual responsibilities although there are areas of overlap. Playing a priest gives you access to your chosen deity. However this isn't a oneway street. You need to be a devout worshipper to have the god answer your prayers. Your god's disposition also plays a part in whether your prayers are answered or not. Some deities are more demanding then others.

As an example: You're a priestess of Sunya. You've been meditating daily and communing with your goddess. You pray to her and make an offering of a bouquet of poppies. Your prayer asks for vines to grow and entangle an enemy following your party. Odds are in your favor that She'll look kindly on you and answer your prayer.

However, you're a priest of Uastis, you can't remember the last time you prayed or offered so much as a cat's whisker to her and you even kicked at a stray dog on your way out of town. Now a big hungry mountain lion is eyeing you. Chances are when you begin screaming with Uastis to intervene, she'll be other wise occupied and you'll be lunch.

In other words, TANSTAAFL(there ain't no such thing as a free lunch).

I haven't created spells like for the AD&D priests because to me that feels too limiting. When you choose you're deity, I can make some suggestions but the prayers are up to you. Do keep in mind your deity's portfolio. Arimon, the god of death won't be of much use if you're praying for someone to heal. And Fortunata the goddess of luck, can't grant you the ability to read that scroll in an obscure tongue although she may be able to guide you to someone who can.

There are several ways to worship. Gods appreciate all sorts of offerings from simple prayers or hymn to sacrificial animals. Keep in mind what a deity favors when offering your prayer. A bouquet of flowers will mean more to Sunya or Deros than it would to Tuath or Meran. Remember too that the offering's value to you plays a part as well. A simple shell that you've carried as a good luck piece will mean more to Meran than a pair of shell earrings you just picked up at the bazaar.

While the deities don't get involved in the average mortal's life on a daily basis, all the gods have the ability to send omens and dreams to their worshippers.