Start with the Taping Knife off the Compound
By Myron Ferguson
The best way I have found to reduce tool marks while smoothing out joint compound is to start the motion with the knife off the compound. Let’s say you are smoothing out the fill coat on a repair. Some compound needs to be removed or feathered in better. If the taping knife is first placed on the compound and then pressure is applied as the blade is moved there will be a tool mark right where you placed the knife to start. Even if you try to have the knife moving as it hits the compound and only apply slight pressure there will be a tool mark. But if the knife blade is first place off the compound on the drywall face and is then pulled across the compound there will not be a tool mark left in the compound.
I use this method whenever I am smoothing compound with a taping knife such as blending in seams with outside or inside corners, smoothing out butted seams, outlet repairs and more. I would guess that most tapers use this method without consciously thinking about it. It just becomes a habit.