A prince should not keep faith when doing so is against his interest. A prince should seem to have the qualities of mercy, faith, humanity, sincerity, and religion. A prince should avoid being despised and hated - A prince becomes hated by taking the property and women of his subjects. He becomes despised by appearing changeable, frivolous, effeminate, timid, and irresolute. He should show grandeur, spirit, gravity, and fortitude.
Conspiracies generally fail.
Fortresses and other things - Do not disarm your own state. Disarm a new state, when you already have an old one. Machiavelli does not recommend encouraging factions in order to keep a principality weak. Former enemies, given a place in the government, can be the most loyal. Fortresses are not safe, in general.