As far as I can tell this works like this:
- You declare your Ready action.
- You place an Aim order token next to your figure.
- You make an attack.
- You remove the Aim order token.
- Your turn ends.
Did I miss anything? It seems to me that the Aim token never persists in any useful fashion: You remove the token when your next turn starts, but you can't combine order tokens so you can't also take the Guard order. This means you need to use the token before your turn ends. And doing anything other than taking an attack means you lose the token.
-K