The way it has usually worked in TW, is that if you fight a lot, your generals pick up good fighting traits (assuming you win!) and that some of these are passed down to sons etc through genetics. I suspect that's still true for M2TW.

I am not sure about governor traits - as M2TW has no influence or acumen stat. In RTW, setting taxes at high and not having too big a surplus (<50k) were important for avoiding bad traits. Having academies was good too. I suspect similar things are going on in M2TW - financial variables will matter, as will some buildings. We are still pretty vague on the details but all will become clear once CA release an unpacker so people can delve into the traits file.

Leaders of crusades seem to get some healthy stat bonuses after successful completion - so putting your faction heir at the head of one has been recommended.