@Jordy_McCroquette avoiding repetition can be difficult, and many authors do seem repetitive. But there are clever ways out of those traps. The advice above is good.
There are differences between the styles of AAR which makes the advice different for each.
Historybook authors, if that's your thing, avoid repetition because they're providing the history and background and setting, and since it's always changing it's not repetitive. Historybook goes from event to event, and it's varied because the events are varied. If a portion of a war, or a period of development, gets boring, then SAY that -- "then there occurred a series of events over a period of 5 years when the country developed and grew...."
Gameplay can be repetitive based on some unfortunate habits:
1. Don't tell us EVERYTHING that happened in the game -- most of us play these games, and we know alot of the scripted events and tech advances. Mention it if it's important, but if it's just another culture tech or artillery advance either don't bother telling us or tell us why it's a big deal -- why it makes it more important than other similar events.
2. Don't explain every little detail, like every skirmish, or the 12th time you've switched taxes up for the middle class. I've written gameplay games where I focus on almost all of the battles in a war, but generally when the game is new and people are wanting to see how the gameplay goes. My current AAR I'm skipping most of the battles and only focusing on really important turning points. Or I'll give a generalized trend my battles are falling into.
Narrative has its own traps:
1. Boring dialogue. There is a place for setting a cozy scene, or establishing a personality or relationship, through an occasional personal chat over events of the day. But if every scene is like this -- "coffee or tea?" "how are the kids?" "What about those Georgians?" -- then it grows stale and doesn't contribute to the story. Mix things up - have some dialogue in snippets while two characters run for their lives, have a conversation in the drawing room, then the next one at a sports event or party. Just be creative.
2. Not every scene has to be with the king/president, or in an office with the cabinet or a secretary present. Switch it up! Have a scene with a housewife, another with a soldier, another with the commander, and another with the cabinet. Have scenes from the enemy point of view. In writing they say SHOW, don't tell. Illustrate the fabric of your story instead of having the president tell you how everything happened.
3. Not every scene has to start when a person enters a room and end when someone leaves a room (or hangs up the phone). Start the scene when things get interesting and end it when they stop. That skips all the useless chatter.
In all of my AARs (be they narrative, historybook or gameplay), I've used screenshots and/or illustrative period art to drive the story. My scenes or descriptions are then built on top of the foundation laid by the screenshots. I find it difficult to read through walls of text. Artwork sets the scene, and it provides something to refer back to, to illustrate what's going on in the text. I take screenshots religiously when I'm playing (I discovered yesterday that I'd hit a 10,000 screenshot limit on my current AAR game and I had to remove them for the game to start playing properly and so I could take additional screenshots). I may discard 95% of the screenshots, or use them only to remind MYSELF of what was going on, so I can better tell the story. Some screenshots show "this is what I was thinking at the time -- this is the information that drove my decision", and thereby help ME write the text in a way that explains what was really going on, even if it never gets posted into the AAR.
Hope this helps! I definitely encourage writers to start an AAR and find their voice. It makes playing more interesting, and draws others into the games also.
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