Steven King in 'On Writing' says everyone has a million words of garbage they have to work through before they write anything good.  Which, I suppose, is another way of saying if you want to get good at something, practice, practice, practice;  the best way to learn is by doing; and similar platitudes.

The secret to writing is rewriting.

The secret to writing is never talk about writing!

(ok the stretchiest Fight Club reference ever)

My record on AAR's is pretty bad, but I've learned a few things, you want to type things down as you're running through the game, specific details can be gleaned from the event log, but what you should be recording is thoughts you have about whats going on from the perspective of people involved with the action. Your own thoughts at least are a must, if something unusual happens, or you make a prediction that may or may not happen later, make a note of it and incorporate that into the thoughts of someone else who was in a position to make that call, or at least someone with that knowledge to pass the information along.
Or write up the AAR as things occur, later going through it and the event logs to get the more dry details.

I classify them into two formats:  those that read like a newspaper report or history textbook, and those that read like a novel.  The difference between "The enemy cruisers launched another salvo of ship-killers" and " 'Missile launch!' screamed Lt. Travers at Tactical.  'Many missiles, impact in fourteen seconds.' "