Oh gee...that's hard to describe. I use a small (getting smaller and more subtle as we go) wrist action, moving palm toward me for "come." (I always practice, while he's staying... touching my nose or scratching my head so he learns that those are not meant for coming...kind of get him use to fine tuning the recognition of the come signal)
Hand out, palm out for wait
Hand out, palm out with a horizontal motion for stay
Hand out, closed fingers, a little up and over his head for sit
Downward motion with forarm, palm down for down.
Palm up and from forearm a raising up to mean sit if he's in a down.
If he's sitting or down and I want a stand, I make my fingers closed like I'm pulling him by a string into the place I want him while saying the word, "stand" or "sit."
Forearm action, hand going down to my side for heel. (like if he is sitting in front, this means he is to come around behind me and sit at heel position) I use my right hand to show him to go toward my right side and he's to go all the way around my body to my left side.
He's just now learning his left and right so I use the words but also point using my whole arm with a sweeping motion from my center all the way to the left or right.
For when he is behind me...way back in a "wait" and I call him up to "heel" while I'm continuing to walk, I use my left arm, palm down, arm back behind my thigh and I swoop it up to my side for him to resume heeling.
Take a bow, it's like down, but I bow too, sort of. I mean I really put the bend in my body too. But of course, with that one, we're still using the word, "bow." It's kind of a new trick.
Back up: short little, repeated jabbing movements with my index finger pointing out, like I'm poking someone. LOL. I use "back, back, back, back" for each step backwards.
Most of these hand signals are automatically learned because they're sort of used when luring with a treat in a lot of cases. If you use the hand signals with the verbal command, there will come a time where just one or the other can be used. Use both while they're learning a skill and they'll catch right on.
I can't think of anything else right now. There are the signals for use in agility but I use the verbal too at this point. A lot of times he can't see me because he's way ahead of me, so the verbal is needed.