First Visit?
In the Orthodox tradition, the faithful stand up for nearly the entire service …. In any case, if you find the amount of standing too challenging you're welcome to take a seat. No one minds or probably even notices. Long-term standing gets easier with practice.
We cross with our right hands from right to left (push, not pull), the opposite of Roman Catholics and high-church Protestants. We hold our hands in a prescribed way: thumb and first two fingertips pressed together, last two fingers pressed down to the palm.
We sign ourselves whenever the Trinity is invoked, whenever we venerate the cross or an icon, and on many other occasions in the course of the Liturgy. But people aren't expected to do everything the same way.
Some people cross themselves three times in a row, and some finish by sweeping their right hand to the floor. On first entering a church people may come up to an icon, make a "metania"–crossing themselves and bowing with right hand to the floor–twice, then kiss the icon, then make one more metania.
To make a prostration we kneel, place our hands on the floor and touch our foreheads down between our hands.
The usual greeting is "Christ is in our midst" and response, "He is and shall be."
Only Orthodox may take communion, but anyone may have some of the blessed bread.
About seventy-five percent of the service is congregational singing.
When the priest or deacon intones, "Let us complete our prayer to the Lord," expect to still be standing there fifteen minutes later.
A constant feature of Orthodox worship is veneration of the Virgin Mary, the "champion leader" of all Christians. We often address her as "Theotokos," which means "Mother of God."
Visiting several Orthodox parishes will help you learn where you're most comfortable. You will probably be looking for one that uses plenty of English in its services. Many parishes with high proportions of converts will have services entirely in English.
(from First Visit to an Orthodox Church, Frederica Mathewes-Green)
Freely Ye Have Received Freely Give