In Drums of Autumn, the fourth novel in the series(1), we get a glimpse into Duncan's grimoire, which includes the following spell; I reproduce it here as it appears beginning on page 692 of the Nook edition of the book:
I raise my athame to the North,
where is the home of my power,
To the West,
where is the hearth of my soul,
To the South,
where is the seat of friendship and refuge,
To the East,
from whence rises the sun.
Then lay I my blade on the altar
I have made.
I sit down amid three flames.
Three points define a plane, and
I am fixed.
Four points box the earth and mine
is the fullness thereof.
Five is the number of protection;
let no demon hinder me.
My left hand is wreathed in gold,
and holds the power of the sun.
My right hand is sheathed in silver,
and the moon reigns serene.
Garnets rest in love about my neck.
I will be faithful.
This would actually be a workable piece, though if I were to test-drive it I would alter the wording a bit to put it more in line with my own praxis (for example, I'd shift the directional attributions a bit, flipping the West and the South as given above). I like the reference to "three flames," which is then amplified by "three points define a plane"; to me this has parallels with the magician's Triangle of Manifestation as well as the symbol of the first degree initiation (at least within some traditions). The four points boxing the earth could easily be the cardinal points that mark the boundaries of the witch's personal universe. Five are the points of the pentagram, which can be used as a protective device. The gold/sun and silver/moon are familiar enough to be nearly self-explanatory. The garnets about the neck have a specific meaning in the narrative (as do the gold and silver on the respective hands), but the wearing of a necklace in ritual is common in BTW-derived witchcraft.
Tweaked to the specifics of one's personal style of working, this incantation might make a fine opening statement before a working. I may try doing just that.
(1) There are many books in this lengthy series of historical time-travel magical fantasy description-defying sagas. If you have the time and the inclination, I recommend them highly.