I played in the Sword one-shot, and we did end up using Fight! But then again, I had a coach who wasn't playing to help me suss it out (only fair, it was three against one!) and keep things moving.
When I played a longer game, we used Fight! a grand total of two times. Both times, it was me against NPCs, so the other players didn't have to worry about it at all. Here's what I did to keep things straight for myself; I'd probably do something similar to teach it to others:
First, I wrote out all the options for scripted actions on index cards. Then I grouped them into levels: Strike, Avoid and Block for the "basic" moves; Charge, Disarm and Great Strike as "intermediate"; and all the other weird little options as "advanced." This was a bit arbitrary — you can tweak which moves were in which level. This felt the most intuitive for me: attack and defense first, then some fancy tricks, then some even fancier tricks.
In play, I began the fight sticking to the first set of moves. Each new volley, I'd evaluate whether I was ready to try a trickier move based on the in-game circumstances, how fluent I was with the actions I was already using, and so forth. My limber Irish Kern was a devil at Positioning, so I as able to dance in and out of range at a whim, but my hits didn't pack much punch. This meant Charge and Great Strike came in quite handy as the duel went on. I think I used Push a couple times, and maybe Disarm once. Feint, Lock and the rest? Never used 'em; there was no need, and I was happy to leave them alone. To this day I have no idea how they work, which is fine!
To teach others this way, I would hand out the basic actions on cards and let them volley with that a bit. If they fight NPCs, then make sure you stick to just those actions, too! No cheating! Introduce a new move, or level of moves, whenever someone's wanting a new tactic — "How 'bout if I just rush the guy and tackle him to the ground?" — or when everyone seems ready. That is, they're really comfortable with the basics. And, again, don't introduce a move yourself as an NPC action; let the players have that advantage. It might be good, though, if the players are stuck ("Man, all we can do is hit and block, we're getting nowhere") to suggest a new tactic and provide the appropriate action.
That all said, moving up to Fight! in a one-shot will usually be a stretch, as folks have pointed out. Whatever you try, good luck!