Well, it does depend on whether you want to use the ictus, or even if you're not super-interested in it, whether your organization definitively excludes binary and ternary counts. I know that one can conduct Dr. Mahrt's style of chant with something approaching Mocquereau's chironomy, and I've seen semiologists conducting from SG manuscripts with something like it, but if you're really not using Solesmes at all, then Mocquereau's way isn't helpful.

There are a lot of good pieces in The Technique of Gregorian Chironomy by Carroll if you really want the ins and outs of the classical Solesmes style (e.g. some of the passages where the notation doesn't make a lot of sense, where there's tension between neumes and where the ictus is printed, where we might be tempted to put an arsis or thesis by default…). But I don't think that it's something to read front to back, and he's a bit too prescriptive, especially on what "must" be an arsis or thesis in cadences. The arsis and thesis rules are in tension, so you must choose one, whereas the ictus placement really does depend on rules and only rarely do I find myself hesitating. I also think that one should try to use square notation, whereas Carroll recommends drawing on transcriptions in modern notation.

@32ContraBombarde has a series on Youtube that I've found helpful.

Jennifer Donelson-Nowicka did a webinar a few years ago that's also on Youtube (I'd tag her for credit, but I fear that I've never mastered tags with spaces in the username…). She has a handout that she starts with that you could probably get by email that teaches the basic rules, shows the drawing, and works through Kyrie XI.

But if I could offer some advice, from a relatively new conductor of chant: if you do use the Mocquereau method, a tight conducting box limited to your torso and absolutely no higher than your chin is essential; except in the dark, where shadows are a problem, I try to keep my stand around my waist, since I usually don't conduct from a Liber (Brevior, Usualis) directly but rather from copies where I can write in the chironomy markings. For the thesis, sometimes, particularly if the schola is awkwardly arranged, you might find yourself drifting, but if you're moving your neck and torso to extend further, you've gone too far… and then my own personal problem: keep it moving, even at the dotted punctum of a ternary rhythm where the "3" follows a half-bar — I tend to get stuck on "2".