The Catholic Church distinguishes two ways in which the Body of Christ is received by the faithful. Saint Thomas Aquinas dedicated an article to this topic (Summa theologiae III, q. 80, a. 1). Moreover, the Council of Trent also treated this subject (Session 13, Chapter 8).
Thomas Aquinas taught that there are two way to receive the Eucharist: spiritually and sacramentally. However, the Council Fathers of Trent teach three ways: spiritually alone, sacramentally alone, or spiritually and sacramentally. As you can see, there is no difference here between Saint Thomas and the Council, but only a further distinction. Here are the words of the Council of Trent:
Now as to the use of this holy sacrament, our Fathers have rightly and wisely distinguished three ways of receiving it. For they have taught that some receive it 1) sacramentally only, to wit sinners: 2) others spiritually only, those to wit who eating in desire that heavenly bread which is set before them, are, by a lively faith which worketh by charity, made sensible of the fruit and usefulness thereof: whereas 3) the third (class) receive it both sacramentally and spiritually, and these are they who so prove and prepare themselves beforehand, as to approach to this divine table clothed with the wedding garment.
So then, if a person is in mortal sin and receives the Eucharist, he receives it only sacramentally but receives no grace, but rather condemnation. Now a person in a state of grace who eagerly seeks union with Christ and makes an act of the will (i.e. an Act of Spiritual Communion), this person does receive the grace and presence of Christ. No then, the best way is to combine both the sacramental reception with the earnest desire of a spiritual communion. This is what spiritual authors call "making a good communion," which requires preparation (sacramental confession or at least an act of contrition) and an openness to receiving the Divine Savior into a the palace of one's heart.
The Council of Trent also gives further advice on how we ought to receive this holy mystery:
Now as to the reception of the sacrament, it was always the custom in the Church of God, that laymen should receive the communion from priests; but that priests when celebrating should communicate themselves; which custom, as coming down from an apostolical tradition, ought with justice and reason to be retained. And finally this holy Synod with true fatherly affection admonishes, exhorts, begs, and beseeches, through the bowels of the mercy of our God, that all and each of those who bear the Christian name would now at length agree and be of one mind in this sign of unity, in this bond of charity, in this symbol of concord; and that mindful of the so great majesty, and the so exceeding love of our Lord Jesus Christ, who gave His own beloved soul as the price of our salvation, and gave us His own flesh to eat, they would believe and venerate these sacred mysteries of His body and blood with such constancy and firmness of faith, with such devotion of soul, with such piety and worship as to be able frequently to receive that supersubstantial bread, and that it may be to them truly the life of the soul, and the perpetual health of their mind; that being invigorated by the strength thereof, they may, after the journeying of this miserable pilgrimage, be able to arrive at their heavenly country, there to eat, without any veil, that same bread of angels which they now eat under the sacred veils.Truly beautiful. When I read such things, I realize how truly unworthy I am to be made a partaker of this great mystery. If the world only knew that God who is Love is present on our altars, would not every last person prepare himself and come kneeling before the throne of grace?
Sacred Heart of Jesus, wounded by our sins, have mercy on us.