I guess what I'm trying to say is that the standard mechanics only help if the map isn't set up like a fortress, and of course some are.
Consider using your blackjack. If guards patrol the room you are in and there is shadow in the same room, then you can probably blackjack camp in that room. Lurk in the shadow until a guard comes in and blackjack it while it's closing the door or on its way out. Stash the body somewhere safe and repeat until no AI has entered that room for some time. Then proceed to the next room and either switch back to casual thievery or continue securing the area depending on prefered playstyle.
A few areas in TDM missions do exhibit layouts and patrols like you would expect them to be like if an experienced guard's captain did his job right. That areas are really hard to ghost by (by intention i would guess). But they are far from being common and you still got your tools and all that movable clutter, authors place in their missions. Apart from blackjack camping (wich is absurdly effective in stealth games in general - to the point where it feels like cheating if you do it in non-fortress areas), there are:
- Bait: Turn off some light and wait in the shadows near that switch. Blackjack the guard as it tries to turn that light back on. Also works with doors left open and rope arrow ropes. Light baiting and door baiting obviously don't work with AI that isn't configured to react to such things (but in fortress-like areas they likely are configured to react).
- Patrol pattern timing manipulation: Distract a guard using a noisemaker, opened door, thrown clutter... to make it leave his patrol pattern for a short time so its pattern becomes out of sync regarding the patterns of other guards. Use the tactic to turn efficient patrol timings into inefficient ones. Patrols might get resynced at certain points on the map, but most authors do not bother to implement that.
- Indirect water arrow torch removal: Aim a water arrow at the ceiling above a torch-wielding guard to extinguish the torch without alerting the guard (in most missions, it will just drop the torch and continue its patrol). Also works with a nearby wall if the water from the arrow reaches the torch while falling down. I experienced a guard wich came back with a fresh torch after i extinguished its old one and let it complete his patrol once (you can still use the darkness right after dousing his torch though).
- Imprisonment: Drop two movables in front of a door so that they block each other to prevent that door from opening towards the movables. Always works when using crates on any moving door with any AI trying to open it. This probably is bug-using at least (probably even considered cheating by most). AI will not cry for help in such situations. The door will try to push the movables aside but the physics engine doesn't handle inertia propagation past the first blocking movable. The guard sometimes tries to use another way though, so make sure to apply that tactic to an already cleaned room that only features one exit just after the AI entered it. I only use that method as a last resort when the author throws un-ko-able AI or arbitrary knockout restrictions at me.