In Dishonored, if you’re trying to play through a game using stealth, then you’re going to want to knock people out instead of killing them in order to get low chaos if you want to get the good ending.
There are two ways to knock people out in Dishonored, which are to use the choke from behind, or to use sleeping darts.
Choking people is a lot more controlled than sleeping darts. To choke someone, you just need to sneak up behind them quietly then press and hold RB on the Xbox 360, or R1 on the PS3. It doesn’t matter if you have your weapons sheathed of not, it will always choke them when you press and hold that button.
It will take a few seconds to knock someone out, so always make sure you have ample time to not only get them choked, but to drag and hide their body as well.
One of my favorite tactics when choking people is to use it immediately after a Blink. For example, let’s say you’re trying to take out a few guards, but you have to cross an open area to get to one. If you time it right, you can blink across the open area and hold the choke button while you’re blinking so that the choke goes off right as you get to them. You can also use this to blink down from a high point and choke, as well as blinking across a hallway for example that has enemies to choke an enemy on the other side, as long as your “landing” spot can’t be seen by other enemies.
Using sleeping darts can work in a pinch, but you have to be much more careful. It’s much harder to control since you can’t always see the line of sight from them to others that might see them. If you use a sleeping dart on someone and another character sees them fall, it will alarm them and anyone else around. It’s much safer to sneak and choke, or Blink + choke in most circumstances.