Oddly, sometimes guards carry goods that can be pick-pocketed, but not looted. If you're looking for a little extra coin, take a second to rob someone before knocking them out. Also, some guards, particularly those carrying documents or firearms, can be pick-pocketed more than once. Civilians can be pick-pocketed without apparent repercussion (unless, of course, you're seen)
The Ol' Walk-And-Don't-Talk:
When choking a hostile into submission, don't wait for unconsciousness to drag them into shadows. You can start moving them around the moment your elbow hits throat, which is extremely useful for guards out in the open, or leaning over balconies. Also keep in mind that you don't need to be right next to someone to initiate the takedown- as soon as you see the onscreen prompt you'll automatically leap into range when you hit the takedown button, which can save valuable seconds in a tight situation. Another second-saver is dragging someone over the edge of a platform or railing as you're choking them- you'll both fall the ground, but if you hit CTRL immediately after, you can knock them out with a single punch to the face that still doesn't count as detection.
The drop-attack is almost completely silent. As long as you're not observed, you can even drop down on the rearguard of a patrol and eliminate him while his fellows are just yards away.
The Importance of Potty Breaks:
In recent years, many videogame enemies have taken to musing out loud about the status of their genitals, and various diseases related thereto. Dishonored 2 is not without such unwanted updates, but even as you mentally filter out this TMI, keep your ears pricked for guards complaining about how much they have to pee. Because these guards are about to leave their post or position and look for a secluded area away from prying eyes for a few moments. Which is to say, these are guards are prepping themselves for an unseen takedown. Don't let the opportunity go to waste.