I'm going to be doing this massively to build up for my shounen mangas. Sort of a combination of fight choreography and sequential art.
Basically in whatever sequential format you like, draw (or write!) a fight scene between two or more characters.
The idea is not only to practice framing of particular action shots but to accurately convey the sequence of combat actions.
i.e. if the character has just blocked a shot with his left arm, he won't punch with it in the next shot, sorta thing :P
You dont have to draw an entire fight if you dont want to or if you can't think of anything, just a couple of frames is also acceptable.
I'm going to try and sort of randomly pick different types of weapons and give them to random A and B characters to duke it out, and see if that helps. Not sure how much narrative to add at this point. Probably I'll keep it minimal to make sure the art is clear what's happening.
It can also be a fight between a character and a monster/animal as well, which is also quite relevant for fantasy manga.
An easier challenge for those who might find it daunting : draw a single shot of combat, a person throwing a punch or two characters with swords clashed etc