When the Battle Planner screen pops up, you get a general list of what you suspect the AI may do. I just click through each of my options. A plan with no added color outline is neutral. A plan with a red outline may put your forces at the mercy of an enemy plan. A green outline gives you the advantage. After checking them all, I choose the one with the best advantage. However, the colored choices only grant an advantage to one possible plan of the three you suspect, so I don't pick a green plan if it might give me a disadvantage to the other two AI choices.
I'm the 51st shade of gray. Eat, pray, Charge!