There are no special pre-requisites for erasing Windows Phone devices. It is not required to for example set up the device before erasure (e.g. select language, accept terms of use, set time and data, sign in to Microsoft account).
In Blancco Mobile 2.0 - 2.0.3, factory rest must be done before starting erasure.
From Blancco 5 Mobile 2.0.4 onwards, factory reset must done after erasure is started.