Since the implementation of pilots, bravery has become a much more important stat. It's very useful to have a team of high bravery pilots for every base, and so training soldier for bravery is more important than it use to be.
The thing is, training bravery is not as easy as training other abilities. Most stats can be casually improved to high levels just by doing ordinary things in missions, without any special effort. (There are ways to accelerate the improvement of any stat, but generally it's enough to just equip gear that will help with the stat you want to improve... eg. carrying a couple of boom fruit can give you the opportunity to improve your throwing without too much effort. Carrying a fast weapon (particularly a fast melee weapon) can give you plenty of chances to improve reactions, etc.
But bravery, in my experience, doesn't improve much beyond ~60 through normal play. The only way I know of to reliably improve bravery is to keep a soldier's moral low for several turns; and that tends to only happen if I'm doing something special to deliberately keep their moral low - such as making them wear a slave outfit and shooting them myself; or doing lots of psi attacks with the witch outfit; or taking combat drugs (and using smokes to boost moral if moral isn't high enough to take the drugs to drop the moral!)
However, I'm pretty sure I've seen soldiers get bravery increases without their moral having been low. So I'm thinking that there must be some other way to train it. Maybe something to do with healing things? Or some particular weapon? I don't know.
I'd prefer to be able to train bravery with just a few tweaks to normal play (such as using a particular weapon), rather than having to do weird stuff like shoot my own soldiers. So I'm wondering, what are the best ways to train bravery?
Before pilots, I didn't bother trying to train bravery at all; because no one panics anyway in an ordinary mission. There's too much moral bonus from killing enemies or from +bravery armour for moral to ever be a serious issue. On higher difficulties it seems that bravery is even less important, because there's just more stuff to kill - and hence boost moral!