Bowing - signifies reverence, respect, and gratitudeĀ
Genuflect - a sign of adoration; bring your right knee to the floor (like kneeling on one knee)
3 Reasons Catholics Genuflect (Fr Mike Schmitz, 5:24)
Kneel - sign of penance, homage, and adoration
Praying in unison (together) - The assembly pray and sing together. This means we are truly one Body united in Christ through the Sacrament of Baptism
Procession - a sign of the pilgrim Church, the body of those who believe in Christ, on their way to the Heavenly Jerusalem.
Sign of the Cross - It was by His death on the Cross that Christ redeemed humandkind.
Sign of the Cross (during the Gospel reading) - We trace the Sign of the Cross on our foreheads, lips, and hearts, praying that the Word of God may be always in our minds, on our lips, and in our hearts.
Being Silent - "Silence in the Liturgy allows the community to reflect on what it has heard and experienced, and to open its heart to the mystery celebrated."
Singing - Singing together in church expresses the sacramental presence of God to His people.
Sitting - the posture of listening and meditation.
Standing - a sign of respect and honor.
This is done only by the priest when we pray or sing the Lord's prayer (the "Our Father") during a Mass. The priest is standing in persona Christi, in the orans posture, speaking to God on our behalf.
The laity and everyone else should not do the orans posture during Mass.
This may be allowed in countries where its Conference of Catholic Bishops allows it.
Receiving the Holy Eucharist
Watch this video on how to properly receive the Holy Eucharist.