The best advice many of us ever received was to just watch and listen, and don’t feel compelled to try to follow along at first.
Really, you can just watch and listen and give glory and thanksgiving to God interiorly! 

There are differences between a Low Mass, a High Mass, and a Solemn High Mass.
The differences are explained here, but in general a Low Mass has just two candles lit, no incense, just one or two altar boys, and is a quieter Mass. 

If it is a High or Solemn High Mass, parts of the Mass are sung and sometimes liturgical actions happen simultaneously with the priest saying some prayers silently while the schola sings others.
In the Novus Ordo (Ordinary Form) we are used to things always happening sequentially, so this can be confusing when new to the Traditional Latin Mass if you are trying to follow along. There are guides in each of the posts of the Mass texts in English to help give you clues to where we are based on where the priest is standing or what he is saying or doing.

Mass is celebrated ad orientem, with the priest leading the congregation in prayer toward the East and toward God.
When the priest is speaking to God, often as an intermediary for us, he faces God both on the altar Crucifix and in the Tabernacle. When he is speaking to us, he turns around to face the people.

You don’t need to know Latin to participate!
Most people at the Mass probably don’t know it either, and you have the English in here so you can follow along and pray the Mass or parts of the Mass with the priest if you want. The epistle and Gospel of the day—“the readings” in the Novus Ordo—are often read by the priest in English on Sundays before the sermon.

While this website has posts with both the unchanging (the “ordinary”) and variable (the “propers” or readings for the Mass) together, most hand missals do not.
If you are using a hand missal (often parishes will hand them out), you will need to go back and forth between the ordinary and the propers.  This is why parishes sometimes have print outs of the propers on Sundays. The tricky thing is that some of the most popular hand missals that parishes use will preprint the propers in the missal for the Feast of the Holy Trinity.

The propers are the Introit, the Collect, the Epistle, the Gradual and Alleluia or Tract, the Gospel, the Offertory, the Secret, the Preface, the Communion verse, and the Post-Communion verse.

Whenever Father is at the Missal on either the far right (epistle-side) or far left (gospel-side) of the altar, he will be reading or singing one of the propers. Only the Offertory, Secret and Preface are read and / or sung with the Missal in the center. 

There are tips along the way in the booklet about when to kneel, sit or stand, but it’s okay to just follow along with everyone else.
There are no rubrics for what the people do at Mass in the Extraordinary Form, but the Mass text posts on this website contain tips for what are some local customs in our area of the U.S. at least. 

The sacred ministers, altar boys, and/or schola make all of the responses on our behalf.
At a Low Mass you won’t really need to say anything except the “Domine, non sum dignus” (pp. 44-45) and the Leonine prayers after Mass. At a High Mass, you may if you wish also join the choir in singing the “Et cum spiritu tuo’s,” Kyrie, Gloria & Credo (if any), Sanctus, and Agnus Dei. These are noted in the Mass text posts. But again, there are no rubrics for the people in the Extraordinary Form and many parishes or countries have their own customs.

You don’t have to wear a mantilla or head covering if you are a woman.
It is a pious custom, but it’s not required and no one will think twice either way.

Communion is received on the tongue, kneeling, and you do not say “Amen.”
The priest prays a beautiful prayer over you with the Sacred Host as you receive Communion and he says Amen at the end. You silently receive our Lord.

This Mass is your patrimony as a Roman Catholic and we are glad you are here!
We hope that this website can help you make the Extraordinary Form an ordinary part of your Catholic life! Deo gratias!