Cerberus,
It's a tricky balance. You don't want to go 'play-by-play' action. Nor do you want to overcontrol. Even the fastest action can be slowed down by too much description.
Being too vague on the other hand, is an issue to. You want to describe the action, but leave room for the reader to imagine it in his mind, see it through your words.
Check out a few writers you enjoy reading, who include combat in their writings, and see how they do it, and why it works for you. Use that as a basis to form your own technique to writing action scenes.
I say this, as I am not sure there is really any way to tell a writer how to write action/combat well, other than a few guidelines.
If you need a few suggestions for authors, let me know the kind of combat you're looking at, and even the POV used, and I'll post a few here.
R-Tech