Eucharistic discipline is the term applied to the regulations and practices associated with an individual preparing for the reception of the Eucharist. Different Christian traditions require varying degrees of preparation, which may include a period of fasting, prayer, repentance, and confession.
Sufficient spiritual preparation must be made by each Roman Catholic prior to receiving Holy Communion. A Catholic in a state of mortal sin should first make a sacramental confession: otherwise that person commits a sacrilege. A sacrilege is the unworthy treatment of sacred things. Deliberate and irreverent treatment of the Eucharist is the worst of all sacrileges, as this quote from the Council of Trent shows:
"As of all the sacred mysteries ...none can compare with the ...Eucharist, so likewise for no crime is there heavier punishment to be feared from God than for the unholy or irreligious use by the faithful of that which...contains the very Author and Source of holiness." (De Euch., v.i).
The above applies to both Latin and Eastern rite Catholics. In addition, they abstain from food and drink (except water and medicine) for at least one hour before receiving, and believe truly in the Real Presence of Christ in the Eucharist. The discipline for Eastern Catholics generally requires a longer period of fasting and some Latin Catholics observe the earlier (pre-1955) discipline of fasting from the previous midnight.
The canonical discipline of the Latin Church is found in Book IV, Part I, Title III, Chapter I, Article 2 (Participation in the Holy Eucharist) of the 1983 Code of Canon Law. The particular applications of Canon 915 have been quite controversial in recent years, while canons 916 and 919 have not stirred as much controversy:
The Oriental canon law of the Eastern Catholic Churches has exactly the same rule regarding the obligation to receiving the sacrament of Penance or Reconciliation before taking Communion, while the rules regarding fasting, prayer and other works of piety vary somewhat in accordance with the tradition of each Eastern Church. The rules of the Eastern Catholic Churches of Byzantine tradition correspond to those of the Orthodox Church, as detailed in the next section.
Orthodox Christians are required to fast from all food and drink and abstain from marital relations in preparation for receiving the eucharist. The fast commences, depending on local custom, no later than when the retiring to sleep the preceding evening and no later than midnight, or even from vespers or sunset the night before. The abstinence from marital relations extends through the preceding day (for which reason married priests may not celebrate the divine liturgy daily), and in some places (notably in Russia), a married priest sleeps in a separate bed from his wife the night before celebrating the liturgy. Fasting in monastic practice is often more strict. During this fasting period, many faithful keep a period of quiet reflection by, for example, abstaining from or limiting television and other entertainment, and by reading devotional literature. Fasting is relaxed for pregnant and nursing women, the ill, the elderly, and young children. It is a matter of some controversy whether or not a menstruating woman may receive the eucharist, with very traditional churches not allowing her to even enter the nave of the church or receive any of the sacraments except on her deathbed, while other churches may totally disregard this custom. Likewise, a man who is bleeding, for instance from a recently extracted tooth, also may not commune.
One who communes infrequently must go to confession beforehand, while one who communes on a regular basis does confess, but the frequency varies by local custom and whatnot. However, for those who are mentally or physically incapable of communicating their sins to a priest, absolution is given without confessing, and for babies and young children even absolution is dispensed with.
In some parts of the Russian church, there is a custom before receiving holy communion that, in addition to reading the evening and morning prayers and attending vespers the night before, reading three devotional canons and an akathist. The canons are usually to Christ, the Theotokos and the guardian angel. There is a custom, among those who have the liturgical resources, to chant the following canons according to the day of the week:
In all Orthodox churches, special prayers before and after communion are recited by the faithful before and after the Eucharist. In current practice, at least a portion of the pre-communion prayers are often recited during the divine liturgy. These prayers express humility and the communicants' sense of unworthiness for the gift they are about to receive. The post-Communion prayers are often read aloud by a reader or a member of the congregation after the liturgy and during the veneration of the cross, these prayers of thanksgiving expressing the communicants' joy at having received the holy mysteries "for the healing of soul and body".
From the American Book of Common Prayer 1979
The Holy Eucharist is the sacrament commanded by Christ for the continual remembrance of his life, death, and resurrection, until his coming again. The Eucharist, the Church's sacrifice of praise and thanksgiving, is the way by which the sacrifice of Christ is made present, and in which he unites us to his one offering of himself. The Holy Eucharist is called the Lord's Supper, and Holy Communion; it is also known as the Divine Liturgy, the Mass, and the Great Offering.
The outward and visible sign in the Eucharist is bread and wine, given and received according to Christ's command. The inward and spiritual grace in the Holy Communion is the Body and Blood of Christ given to his people, and received by faith. The benefits we receive are the forgiveness of our sins, the strengthening of our union with Christ and one another, and the foretaste of the heavenly banquet which is our nourishment in eternal life.
Prior to receiving the Eucharist, it is required that we should examine our lives, repent of our sins, and be in love and charity with all people.
However, some Anglicans and Episcopalians, especially Anglo-Catholics and those of the High Church party, observe the practice of fasting for one hour before receiving Communion, while others abstain from any food or drink from midnight until the time of communing.
Lutherans are taught to prepare to receive this sacrament through prayerful reflection upon their sinful nature, their need for a Savior, the promise that their sins are forgiven for the sake of Jesus' death on the Cross, and that the Eucharist gives this forgiveness to them. "Fasting and bodily preparation are indeed a fine outward training," Martin Luther said, "but he is truly worthy and well prepared who has faith in these words, "given and shed for you for the forgiveness of sins." 
The Evangelical Lutheran Church in America, the largest Lutheran denomination in the United States, practices open communion, offering the Eucharist to adults without receiving catechetical instruction, provided they are baptized and believe in the Real Presence.
Some Lutherans practice closed communion, and require catechetical instruction for all people before receiving the Eucharist. Failing to do so is condemned by these Lutherans as the sin of "unionism". These Lutheran denominations restrict communicants to members of their own Synod and those churches and Synods with whom they share "altar and pulpit fellowship", which may mean excluding even other Lutherans from Eucharistic reception.
The timing of First Communion also varies. Historically, First Communion was delayed until after an individual had completed catechism classes and been confirmed, but gradually the timing of First Communion shifted so that it was administered before Confirmation rather than after, following the Roman Catholic tradition. In many Lutheran churches, the average age of first communion is somewhere between the ages of seven and ten, though a considerable number of Lutheran churches offer First Communion even earlier. In North America, the time for administering First Communion is usually determined by the parents in consultation with the local pastor, but some Synods may have guidelines which prevent communion before a specific minimum age.
The Doctrines and Discipline of the Methodist Church specifies that "Upon entering the church let the communicants bow in prayer and in the spirit of prayer and meditation approach the Blessed Sacrament."
In Methodism, the table is made available to all people, and none are turned away. This practice is referred to as keeping an "Open table". The general invitation is typically made in the ritual, "Christ our Lord invites to his table all who love him, who earnestly repent of their sin and seek to live in peace with one another." All are free to communicate at the appropriate time.
Unbaptized persons who respond to the invitation are urged to be instructed in and receive baptism as soon as possible, as Methodism recognises that in normal circumstances, baptism should be a prerequisite to a person's partaking in the Eucharist.
Among Presbyterians, there is neither requirement, nor prohibition, of any of the traditional understandings of what it means to "make ready": it is left to local custom. In modern times, there is no uniform practice of earlier patterns of fasting, public or private prayer, or the preparatory service (Vespers).
However, the Westminster Larger Catechism has rather extensive instructions on how those who "receive the sacrament of the Lord's supper are, before they come, to prepare themselves unto . . . ." Specifically, they are to prepare "by examining themselves of their being in Christ, of their sins and wants; of the truth and measure of their knowledge, faith, repentance; love to God and the brethren, charity to all men, forgiving those that have done them wrong; of their desires after Christ, and of their new obedience; and by renewing the exercise of these graces, by serious meditation, and fervent prayer." Westminster Larger Catechism, Q. 171.
Therefore, the Presbyterian Church in America's Directory for the Worship of God advises that a week's notice be given to the congregation prior to the administration of the Lord's supper: "It is proper that public notice should be given to the congregation, at least the Sabbath before the administration of this ordinance, and that, either then, or on some day of the week, the people be instructed in its nature, and a due preparation for it, that all may come in a suitable manner to this holy feast." PCA Book of Church Order, Directory for the Worship of God, ch. 58, para. 3.; see also Presbyterian Church (U.S.A.) Book of Order, Directory for Worship, W-3.3609 (requiring one week's notice if the sacrament is not observed weekly); Orthodox Presbyterian Church Book of Church Order, Directory for the Public Worship of God, ch. IV, para. 1. (requiring "adequate preparation").
The Westminster Larger Catechism also provides extensive instructions on "what is required of them that receive the sacrament of the Lord's supper" during and after its administration.