Sorry for a bit of a bump, I'm new here and I don't want to get on a bad list during my second day.
For me, my fights started improving when
A: I watched some of the pros action scenes, very cool, taught me to be more imaginative.
B: PRACCCTICE!!! It just takes practice, time, work, and lots of it, NO ONE becomes an expert Lego animator overnight, it just takes time.
C: Finally, ( and very importantly ) PLAN YOUR SHOTS, timing is critical and without good planning it cannot be achieved. Plan the shot, PLAY IT OUT, really, play with the figures fighting each other, it will always be more imaginative when you do that rather than making up the fight as you go along. Then memorize what you did and animate it, your timing and imagination will be much better. 