Things you just never do in battles.

[Martok]

I couldnt think of any decent "Never" battle anecdotes so i`ll contribute a campaign one.

Never, ever conquer the Byzantine Empire before the Mongols show up

It's all about location, my friend. Like Caravel, I don't necessarily take out the Byz, but I will make sure to grab Georgia & Constantinople (along with the rest of Asia Minor) and then fortify those two spots like it's going out of style. So long as you can do that, destroying the Byzantines isn't necessary.

Never engage a byzantine army led by a 7 star or more Kata general,those things can really be a pain..

Crossbow/arbalest bolts. Lots and lots of them.