One important thing to know, is that the Divine Liturgy is usually preceded by an hour to an hour-and-a-half service called the Orthros (or Matins). This is a prayer service conducted mostly by the reader(s), but also with a little bit of participation with the priest. People will not usually be there at the beginning of this service, they will come in sometime in the middle of the service instead.
If you decide to go to the church during the Orthros, just know that to walk into the nave while the six psalms are being read or the priest is censing the icons is usually considered poor form. If you walk in while these events are occurring, stay in the narthex and wait until after the priest finishes censing or the reader finishes reading the six psalms. The priest may also walk out into the narthex and cense the icons and any people who might be standing in the narthex at that time. Should that happen, stand reverently and cross yourself when the priest censes in your direction (this of course can all be avoided if you show up when the Orthros begins).
After the Orthros is finished, then Divine Liturgy begins with the priest saying, “Blessed is the kingdom of the Father and of the Son and of the Holy Spirit, now and ever and unto ages of ages.” The Church will usually have an estimate of when the Divine Liturgy will start (the website will say something like Orthros 8:15, Divine Liturgy 9:30), although it won’t be completely accurate, as the Divine Liturgy starts whenever Orthros ends. It’s considered to be poor form to show up late for the Divine Liturgy, and it is strongly discouraged, even though you will see people who show up late (just like the stragglers who show up late for mass). The Divine Liturgy can last for an hour-and-a-half to two hours, depending on a number of factors.
The Divine Liturgy is divided into two parts, the Liturgy of the Catechumens and the Liturgy of the Faithful. The Liturgy of the Catechumens is divided up into several parts. The Liturgy of the Catechumens contains the gospel readings, and usually the homily (although the homily may come before dismissal). The Liturgy of the Faithful is when communion is taken (of course, communion is only available for those who are members of the Eastern Orthodox Church).
You will likely get lost, but for the most part, it’s easier to just experience it the first time without trying to follow along hopelessly in with the rubrics. We use the sign of the cross a lot more than Roman Catholics do. People typically cross themselves whenever the line “Glory to the Father, and to the Son, and to the Holy Spirit,” is said, whenever the trinity in general is mentioned, whenever the cross is mentioned, whenever the Theotokos is mentioned, whenever the priest censes in their direction, when the bread and the wine is brought out from behind the iconostasis, and sometimes when saints and martyrs are commemorated. Honestly, if you just watch what other people do and just try to follow along, you should be fine.
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