Reverences
Take care always to make the appropriate reverences in coordination with the other servers and the altar party: bowing, genuflecting, striking the breast, and singing the cross at the proper moments.
Important forms of reverence include the following:
Signing the cross
When making the sign of the cross, begin with the joined-hands position. Then place the left hand, extended, with the fingers and thumb held close together, on your chest, just below the breast. Make the sign of the cross with the right hand. Without bowing your head, touch your forehead with the tips of your three longest fingers fully extended and held close together, then, in sequence, touch the center of your chest (above your left hand), your left shoulder, and then your right shoulder. Immediately resume the joined-hands position. Servers with anything in their hands at any time during Mass do not cross themselves. You do not make the sign of the cross when genuflecting.
Genuflecting
Genuflection is normative and should be habitual when passing before the tabernacle whenever the Blessed Sacrament is present, as signaled by the sanctuary light. Typically, the Blessed Sacrament is always reposed in the tabernacle except on Good Friday.
When making a simple genuflection, touch the right knee to the ground, close to the heel of the left foot. Do not bow the head or prop a hand on the floor. Hold your body steady and perfectly erect. Hold the head straight - even at the name of Jesus - since the act of reverence is fully expressed by the bending of the knee and not by a superfluous bow of the head or body. Insofar as you are physically able, maintain the joined-hands position at the breast throughout the genuflection.
Genuflections are made whenever arriving at or leaving the foot of the altar, at the Incarnatus in the Creed, and whenever the missal stand is transferred from one side of the altar to the other.
Bowing
In liturgical actions, in general, there are three bows: simple, moderate and profound. Servers need to learn the right moments and degrees of bowing by paying particular attention to the example of the MC or acolyte, both of whom will generally cue the appropriate gesture.
The simple bow is a bending of the head only. This bow is made (1) to the cross, (2) at certain points in the liturgy, most notably, "we worship thee" and "receive our prayer" in the Gloria, (3) at the mention of the name of Mary, and (4) at the mention of the name of a saint in the mass celebrating his or her particular feast day, especially when that saint's name is mentioned in the Collect and/or in the Canon of the Mass. Servers holding processional candles or the crucifer when carrying the processional cross typically bow only by slightly nodding the head. When another person has taken something from you, or given something to you, or has done some service such as incensing you, or you have done some service to another, bow to that person. It is also customary for the thurifer and whomever he will incense to bow to each other before the incensing. Servers should take care to offer and return bows at the altar, as prompted, when serving the cruets and helping with the ablutions.
The moderate bow, as the designation implies, is never excessive, consisting of a bowing of the head and slight rounding of the shoulders so that, while standing, you should just see your feet. We make a moderate bow (1) at the name of Jesus, and (2) toward an altar when the Blessed Sacrament is not present.
The profound bow is a deep bow from the waist, with hands lowered to the thighs if not holding anything. We bow profoundly at the Gloria Patri and other such invocations of the Trinity such as during the Introit.
We do not typically bow while kneeling, with the notable exceptions of the General Confession, the Prayer of Humble Access, and during the Prayer of Consecration, as prompted by the Sanctus Bell.
Striking the breast
It is customary to strike the breast with the right hand, closed, at the following times:
During the General Confession, thrice, at the words "thought, word, and deed"
At the Agnus Dei, three times, at the phrase “the sins of the world”
At the Non Sum Dignus, with each refrain of "Lord, I am not worthy."
In striking the breast, you should do more than merely brushing your chest with the tips of your fingers, but at the same time the gesture should not be an exaggerated thud either.