The Feast of St Gabriel the Archangel is on March 24th (last recorded date before it is moved to coincide with Michaelmas, Feast of the Archangels). There seems to be some confusion over when one starts a novena leading up to a Saint's day: do you finish your ninth day of prayers on the Saint's day or do you finish the day before? Not sure. I like the idea of finishing the day before, and leaving the actual Saint's day for simple prayers and offerings.
Whichever version works for you. Start your prayers on March 15th if you want to finish the day before, or on March 16th if you want to finish on the Saint's day.
The Archangel Gabriel is one of the three canonical Archangels (the other two being Michael and Raphael) and appears in both the Old and New Testaments. His name means "strength of God" and He is the patron of messengers, ambassadors, telecommunication workers, postal workers (some add parents and teachers). He is perhaps most famous as the Angel of the Annuciation (New Testament) and as the Angel of Revelation (Islam).
If you've been following along with recent occult discourse, you should realize that saints and angels both pre-date the Abrahamic faiths that have adopted them as their standard bearers. Messengers of God and the Mighty Dead both most likely reach back to our earliest ancestral worship and magic. Embrace them. Leave the hang ups behind and reclaim your birthright as a human.
Prayer to St Gabriel the Archangel
O blessed Archangel Gabriel, we beseech thee, do thou intercede for us at the throne of divine mercy in our present necessities, that as thou didst announce to Mary the mystery of the Incarnation, so through thy prayers and patronage in heaven we may obtain the benefits of the same, and sing the praise of God forever in the land of the living.
Amen. - source unknown
NOVENA TO SAINT GABRIEL, ARCHANGEL
Saint Gabriel the Archangel, I venerate you as the Angel of the Incarnation, because God specially appointed you to bear the messages concerning the God-Man to Daniel, Zechariah, and the Blessed Virgin Mary. Give me a very tender and devoted love for the Incarnate Word and his Blessed Mother, more like your own.
I venerate you also as the “Strength from God”, because you are the giver of God’s strength, consoler and comforter chosen to strengthen God’s faithful and teach them important truths. I ask for the grace of a special power of the will to strive for holiness of life. Steady my resolutions; renew my courage; comfort and console me in the problems, trials and sufferings of daily living, as you consoled our Savior in his agony and Mary in her sorrows and Joseph in his trials. I put my confidence in you.
Saint Gabriel, I ask you especially for this favor: (mention your request). Through your earnest love for the Son of God made man and for his Blessed Mother, I beg of you, intercede for me that my request may be granted, it it be God’s holy will.
Pray for us, Saint Gabriel the Archangel. That we may be worthy of the promises of Christ. - From Novena.com
Angelus Domini (The Angel of the Lord)
V: The angel of the Lord declared unto Mary,
R: And she conceived by the Holy Spirit.
Hail Mary...< br/> V.: Behold the handmaid of the Lord,
R: Be it done unto me according to Thy word.
V.: And the Word was made flesh,
R : And dwelt among us.
V: Pray for us, O holy Mother of God,
R.: That we may be made worthy of the promises of Christ.
Let us pray
Pour forth, we beseech Thee, O Lord, Thy grace into our hearts, that we to whom the Incarnation of Christ, Thy Son, was made known by the message of an angel, may by His passion and cross be brought to the glory of His resurrection. Through the same Christ our Lord. Amen. (Tradional, prayed 3 times a day at 6 Am, 12 PM and 6 PM)
Conjuration of Gabriel
I CONJURE and confirm upon you, ye strong and good angels, in the name Adonai, Adonai, Adonai, Adonai, Eye, Eye, Eye; Cados, Cados, Cados, Achim, Achim, Ja, Ja, strong Ja, who appeared in mount Sinai with the glorification of king Adonai, Sadai, Zebaoth, Anathay, Ya, Ya, Ya, Maranata, Abim, Jeia, who created the sea, and all lakes and waters, in the second day, which are above the heavens and in the earth, and sealed the sea in his high name, and gave it its bounds beyond which it cannot pass; and by the names of the angels who rule in the first legion, and who serve Orphaniel, a great, precious, and honourable angel, and by the name of his star which is Luna, and by all the names aforesaid, I conjure thee, Gabriel, who art chief ruler of Monday, the second day, that for me thou labour and fulfil, &c.
-- from The Heptameron, courtesy of Esoteric Archives and the awesome Jospeh H. Peterson
There are likely more prayers available, feel free to search or compose your own (I will one of these days, Gabe and I go way back). Maybe try to throw in the Prayer of Monday from Hygromanteia?