I was taught that we cross ourselves for mention of:
The Holy Trinity (Father, Son, Holy Spirit/Ghost)
When the name of the Lord is blessed
At the Creed (and within the Creed in the portion about the Holy Spirit being worshiped with the Father and the Son. Some also cross themselves on all the stanzas following that till the end.
The Our Father (and it is my understanding that on weekdays the tradition is to further say this standing on ones knees outside the Paschal season)
The invocations over the Holy Gifts, making a full metanoia at the triple amen (outside Pashcal season if a liturgy is served during the week, then instead of a metanoia (fingers touching the ground) a full prostration is made (face to the floor).
At key places starting and within the confessional prayer before Holy Communion, esp. on the "Like the thief will I confess thee "remember me O Lord in Thy Kingdom", "receive me today as a communicant of Thy Holy Mysteries", and at the end.
Trisagion prayer (full metanoias on the Holy God, Holy Mighty, Holy Immortal One)
Paschal Troparion (Christ is Risen...)
At the reading of the epistle and at the reading of the Gospel.
We also cross ourselves entering the temple, before icons, crossing across the middle of the temple from one side to the other (passing before the Holy Altar), entering the altar (special rules, ask the priest), leaving the temple, when the Holy Cross passes before us, when the Gospels pass before us, and some cross themselves when the Holy Gifts brought before the people prior to their consecration. We also cross ourselves prior to kissing the cross at the dismissal, and it is the general custom to cross oneself before the icon of the Theotokos after communion and clear of the chalice (no bumping), this is a show of gratitude for her permitting us to receive the Holy Gifts...It is like regarded as a personal piety, but it is a very old and widespread one.
I was also taught we cross ourselves in private when passing before a temple while driving or walking past.
We do not cross ourselves:
When the priest is blessing us with his hand or with the Gospel, candles, or with the Holy Chalice. In those situations, we receive the blessing with a bow/inclination of our head and upper body. We also bow before the cross and when during the Divine liturgy the priest elevates the Holy Gifts and says, "Holy things for the Holy"
This was what I was taught...others may have had other variations on the above taught to them (things like prostrating entering and leaving the temple on weekdays, greeting icons, and metanoias when entering temple/cathedral property, etc.)
OK, I'm going to have to ask Fr. M. a few questions, maybe.
There are actually many of these times I recognize that people do cross themselves, though I'm not sure about all of them (some are not done in our church that I'm aware of).
And it depends on who I'm watching. Generally speaking, the older folks cross themselves more often, and the much younger ones almost never cross themselves.
One of the ladies who explains things to me said that we cross ourselves when we pass the church because of the presanctified Body and Blood that are within. I've also been told to do so when entering the Church, or before venerating an icon.
I noticed right away that everyone crosses at the "Christ is Risen" line (in either language) when singing the troparian. The priest also crosses with a candle at that time.
I've actually been closely watching to try to figure out when to cross when the priest blesses us. I'm still confused on that one. Sometimes people seem not to, but maybe I'm watching different people at different times, because I can't figure it out.
I tend to bow AND cross myself whenever he blesses us with his hands or with the book, as long as I see anyone else cross themselves. I'm usually a beat behind. But I'm just not sure.
We bow and
cross when he censes, or passes by with anything, really. And we turn to face as he passes by. When the altar boys carry the cross, the priest censes, passes by with the Eucharist or the Holy Book. Which gets confusing, since the altar boys with the cross precede the Eucharist.
Generally I try to watch everyone else.
Some parts are becoming very natural to me, and others I am not yet sure of.
And of course as far as the seasons, I don't know yet. I began coming just before the beginning of Lent, I believe, so I really only know anything about Lenten season and Paschal season so far. I know there is some difference in days of the week and seasons.
I'm just happy that I (usually) know when to sit and stand. And Fr. M. came to me this week and explained that the first part of Orthros is not in the guide, so I can wait at the beginning of the service. Last week people kept asking me where we were, and I didn't know. It was a bit of pantomiming across the church, LOL, so not good I'm sure.
Much, much, MUCH to learn!
Then again, someone who I hadn't met before asked me last week - she thought I was already Orthodox and came from another church. So at least I don't stand out as badly as I might.
Still, every week there is a question or something I don't get quite right. This week I pulled out the kneeling bar because someone else did (and I hate to make noise with it, so I wait for a good time to lean down and do it carefully) ... then no one else did so I had to put it back up, but I had to wait until a good time to do that quietly too.