I think a long fight scene is just a lot of sequences like that, all strung together. I mean, when Character A gets knocked to the side, is that really it for them? They're not gonna get back up and try again...??
If you're having trouble coming up with additional actions, you could think of it that way, in terms of what each character wants to do. Every action in a battle provokes a reaction; every move has a thought behind it.
I think the best way is to put down whatever you need to see to understand how to draw the scene.
Me, I visualize things very easily, and I enjoy it (and I tend to remember what I see in my head, even years later), so just writing 'A takes down B' is enough to get my brain going in the right direction.
Sometimes, for a particularly fancy fight scene (or for a special move I don't want to forget) I'll write something a little more specific, like 'A kicks B in the gut, then throws him to the ground'. If you have trouble coming up with moves on the fly, you should definitely write down a full list of moves like that, from the beginning of the fight to the end.
If you need a stronger visual aid, you could even storyboard it: panel out the whole fight with stickfigures and little speech bubbles, so you know exactly what to draw when the time comes.
