One of the most challenging trophies to acquire in all of Dishonored 2 has players trying to complete the entire game without killing a single person. This alone sounds like a daunting challenge, but it’s also the best way to get the trophy for never alerting a guard as well. In order to get this, you should make sure that both the mechanics and level design is familiar to you, as it will remove a lot of headaches.
In Dishonored 2, it will behoove you to stay up on the roofs and rafters as much as possible. Staying off the streets will allow you to avoid a lot of patrols throughout Karnaca. Given most NPC’s vision does not extend vertically, this can let you use tall bookshelves and even lamps to hide above enemies. This will allow you to avoid most engagements that could end in bloodshed and help you learn the patterns of the guards in a particular mission. You also rarely want to engage more than one foe at a time unless you are using a power like Bend Time or Domino. Isolating NPCs and hiding them in areas that are no longer patrolled is key to going undetected.
Also, if you are going for this trophy/achievement, then you can play on any difficulty, so attempting the No Kill run on Easy will be far less frustrating. Guards are way slower to react and it will offer more leniency if you make a mistake during your attempt. Finally, make use of your Quick Save function regularly during your playthrough. Usually after each knockout or before you are about to try something fairly risky.