There are a tremendous amount of valuable resources on the internet to aid parish choirs to sing the Propers and the Ordinary at Mass. There is very little on Gregorian hymns.
So where better to start, and on the transferred feast of Corpus Christi, than with the Adoro te devote, one of the five great Eucharistic hymns of St Thomas Aquinas written for the feast of Corpus Christi in 1264 at the request of Pope Urban IV.
Rev Matthew Britt in The Hymns of the Breviary and Missal writes:
The hymns of the Angelic Doctor are remarkable for their smoothness and clearness, and for their logical conciseness and dogmatic precision….. It is fitting that a great Doctor of the Church and a great Saint should have confined his hymn-writingto a single subject, and that, the sweetest and profoundest of all subjects, the Most Holy Sacrament of the Altar
Adoro Te written in Mode V is frequently sung in Benediction at as a Communion hymn. Our parish choir always sing this hymn starting on a D. It is important that when sung it is phrased as four lines, rather than eight. Ignore those quarter bar lines. If sung at a reasonable tempo, you should not need to breathe at the quarter bar lines. Each of the four lines should be sung as a beautiful Romanesque arch of sound rising up to the summit of the high neumes with a graceful crescendo and then back down to the end of each line. As you sing up to the summit of each line, do not be afraid to sing out, particularly in the climatic third line of each verse. Coming back down keep the sound well supported, particularly with the descending clivis’. All this should be sung as legato as possible.
A good tip is to practice singing the last word of each line which is always a dactyl with a lighter middle syllable. In the first verse, these are the rhyming couplets Dé-i-tas and lá-ti-tas and then súb-ji-cit and dé-fi-cit. Be careful not to shorten the final syllable. The first accented syllable must be given its full length, a fraction longer than the non-accented syllables.
Another important point is not to sit too long on the dotted punctums.
The best way to sing hymns is to always sing them antiphonally particularly if you have a mixed choir. The common practice in our choir is to all sing verse One, ladies verse two, chaps verse three and so on with the the final verse sung tutti. When sung in this manner, it makes it much easier to pass fluidly from one choir to the other between verses with no break, in the same manner than psalmody is sung.
(All images are taken from the Parish Book of Chant available for download from the Musica Sacra site.)