These are war strategies that I have developed during two long wars in which unexpectedly backfired on me. These have only really been tested on chieftain, where the AI is comparably dumb to other levels. So they might not work too well. And these are really towards modern warfare.
1) Whatever you do, do it quick: Long wars can drag you into war weariness if you don't allow the government to manage citizen moods and even if you do that it can lead to starvation. Allowing the war to progress on also gives the AI the chance to pillage your roads, maybe starving out your population. If the war is long there'll be more resistance, resentment, and hardship. Though Democracy has the highest war weariness, if you let the governor manage moods it won't be a problem.
