No valour for princesses.

Emissaries are based on your kings influence.

Assassins gain valour by killing targets and with building upgrades (after brothel). There are also hero assassins. One I know of is the English. Make an assassin in ??? 1192 ??? I can not remember the year, but it is early. I have also read that Syria gives a +2 valour to assassins, but this is a hidden trait of the province. The best way to make sure your assassins are successful is to send them in packs of 10. Overkill? not if you want to make sure the deed is done. If you want to kill Catholics, the best way is with Grand Inquistors in packs of 3 -5. Just make sure you get them away from your provinces quickly or they will get bored and start burning you.