Taping down Ethernet cable without damaging paint

These Command Cord Organizer cable management items are fantastic. 3M sells a bunch of different ones (and different sizes). And they remove easy without damaging your paint.

I would buy the proper size staples and using either a gun or a hammer (size) tack the cable where I want it. Done properly, the damage is truly minimal. Encasing it in another conduit, while more protected, will add to the size staples necessary.

Depending on the layout of furniture in the room it might be possible to hide the cable behind/under that and the use rugs to cover it for walk ways (or seeing your edit just gaffa tape it to the carpet, if you do this just be careful as when you peel it up the floor that was covered by tape will probably be cleaner than the floor which wasn't). Or what I've done in my flat is to run some of this trunking along the floor by the wall, the trunking seems to stay where I've left it without any mechanical fixing to the wall.