How to build (and build up) assasins ?

[econ21]

From the original title, I thought the question was "how can I build up assassins?"[1]. My novices get very low chances to kill. In RTW, you had good chances to kill other assassins and so develop your subterfuge. What's the secret in M2TW? Just go for the softest target and with enough assassins, eventually one will take off?

[1]I've now edited the title to include my question.